SOILS   AND   FERTILIZERS 


THE  MACMILLAN  COMPANY 

NEW  YORK   •   BOSTON  •    CHICAGO 
SAN  FRANCISCO 

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TORONTO 


0 
SOILS  AND  FERTILIZERS 


BY 
HARRY   SNYDER,    B.S. 


THIRD  EDITION 


Nefo  ||0rfe 

THE   MACMILLAN   COMPANY 
.    1912 

All  rights  reserved 

398GO 


COPYRIGHT,  1899,  1905, 
BY  CHEMICAL  PUBLISHING  COMPANY. 

COPYRIGHT,  1908, 
BY  THE  MACMILLAN  COMPANY. 


Set  up  and  electrotyped.     Published  June,  1908.     Reprinted 
August,  1909  ;  January,  December,  1911 ;  September,  1912. 


XortoooD 

J.  8.  Gushing  Co.  —  Berwick  A  Smith  Co. 
Norwood,  Mass.,  U.S.A. 


PREFACE   TO   THIRD    EDITION 

THIS  work  is  the  outgrowth  of  instruction  given  at 
the  University  of  Minnesota  to  young  men  who  intend 
to  become  farmers  and  who  desire  information  that  will 
be  of  assistance  to  them  in  their  profession.  At  first 
mimeographed  notes  were  prepared,  which  were  later 
published  under  the  title  "  The  Chemistry  of  Soils  and 
Fertilizers."  This  was  revised,  enlarged,  and  published 
as  "  Soils  and  Fertilizers."  With  the  extension  of 
various  lines  of  investigation  relating  to  soils,  a  sec- 
ond revision  and  enlargement  of  the  book  has  become 
necessary.  It  is  the  aim  to  present  in  condensed  form 
the  principles  of  the  various  sciences,  particularly  chem- 
istry, which  have  a  bearing  upon  the  economic  produc- 
tion of  crops  and  the  conservation  of  the  soil's  fertility. 
The  work  as  now  presented  includes  all  the  topics 
and  the  laboratory  experiments  relating  to  soils,  as  out- 
lined by  the  Committee  on  Methods  of  Teaching  Agri- 
culture, of  the  Association  of  Agricultural  Colleges  and 
Experiment  Stations. 

HARRY   SNYDER. 

UNIVERSITY  OF  MINNESOTA, 
COLLEGE  OF  AGRICULTURE, 

ST.  ANTHONY  PARK,  MINNESOTA, 

March  i,  1908. 


CONTENTS 

PAGES 

INTRODUCTION i-io 

Early  uses  of  manures  and  explanation  of  their  action 
by  alchemists  ;  Investigations  prior  to  1800 :  Work  of  De 
Saussure,  Davy,  Thaer,  and  Boussingault ;  Liebig's  writ- 
ings and  their  influence  ;  Investigations  of  Lawes  and  Gil- 
bert ;  Work  of  Tull ;  Contributions  of  other  investigators ; 
Agronomy ;  Value  of  soil  studies. 

CHAPTER   I 

PHYSICAL  PROPERTIES  OF  SOILS  t  n-53 

Chemical  and  physical  properties  of  soils  considered ; 
Weight  of  soils  ;  Pore  space  ;  Specific  gravity ;  Size  of  soil 
particles ;  Clay ;  Sand ;  Silt ;  Form  of  soil  particles ;  Num- 
ber and  arrangement  of  soil  particles  ;  Mechanical  analysis 
of  soils  ;  Crop  growth  and  physical  properties.  Soil  types  : 
Potato  and  truck  soils ;  Fruit  soils ;  Corn  soils ;  Me- 
dium grass  and  grain  soils ;  Wheat  soils ;  Sandy,  clay, 
and  loam  soils.  (Relation  of  the  soil  to  water)  Amount  of 
water  required  for  crops ;  Bottom  water ;  Capillary  water ; 
Hydroscopic  water ;  Loss  of  water  by  percolation,  evapo- 
ration, and  transpiration  ;  Drainage ;  Influence  of  forest 
regions ;  Influence  of  cultivation  upon  the  water  supply 
of  crops  ;  Capillary  water  and  cultivation  ;  Shallow  surface 
cultivation ;  Cultivation  after  rains  ;  Rolling ;  Subsoiling  ; 
Fall  plowing ;  Spring  plowing ;  Mulching ;  Depth  of 
plowing;  Permeability  of  soils  ;( Fertilizers  and  their  in- 

vi  i  ^ 


Vlll  CONTENTS 

•\  PAGES 

fluence  upon  moisture  content  of  soils  jj  Farm  manures 
and  soil  moisture ;  Relation  of  soils  to  heat ;  Heat  re- 
quired for  evaporation ;  Influence  of  drainage  upon  soil 
temperature  ;  Specific  heat  of  soils  ;  Cultivation  and  soil 
temperature ;  Heat  from  chemical  reactions  within  the 
soil ;  Heat  and  crop  growth ;  Organic  matter  and  iron 
compounds;  Color  of  soils  ;  Odor  and  taste  of  soils  ;  Power 
to  absorb  gases ;  Relation  of  soils  to  electricity ;  Impor- 
tance of  physical  properties  of  the  soil. 

CHAPTER   II 

GEOLOGICAL  FORMATION  AND  CLASSIFICATION  OF  SOILS      54-70 

Agricultural  geology ;  Formation  of  soils ;  Action  of 
heat  and  cold;  Action  of  water;  Glacial  action ;  (^Chem- 
ical action  of  water ;  1  Action  of  air  and  gases ;  Action  of 
microorganism ;  Acuon  of  vegetation ;  Action  of  earth- 
worms ;  Action  of  wind  ;  Combined  action  of  the  various 
agents  ;  Distribution  of  soils ;  Sedentary  and  transported 
soils ;  Rocks  and  minerals  from  which  soils  are  derived, 
as  quartz,  feldspar,  mica,  hornblende,  zeolites,  granite, 
apatite,  limestone,  kaolin ;  Disintegration  of  rocks  and 
minerals ;  Value  of  geological  study  of  soils. 

CHAPTER   III 

/THE  CHEMICAL  COMPOSITION  OF  SOILSJ  .  .  .  71-115 
v-_  Elements  present  in  soils  ;  Classification  of  elements ; 
Combination  of  elements ;  Forms  in  which  elements  are 
present  in  soils ;  Acid-forming  elements,  silicon,  double 
silicates,  carbon,  sulphur,  chlorine,  phosphorus,  nitrogen, 
oxygen,  hydrogen;  Base-forming  elements,  aluminum, 
potassium,  calcium,  magnesium,  sodium,  iron ;  Forms  of 
plant  food ;  Amount  of  plant  food  in  different  forms  in 


CONTENTS  IX 

PAGES 

various  types  of  soils ;  Acid  soluble  matter  of  soils  ;  Acid 
insoluble  matter ;  Action  of  organic  acids  upon  soils ;  How 
a  soil  analysis  is  made ;  Value  of  soil  analysis ;  Interpre- 
tation of  the  results  of  soil  analysis ;  Use  of  dilute  acids 
as  solvents  in  soil  analysis  ;  Use  of  dilute  mineral  acids  in 
soil  analysis  ;  Available  and  unavailable  plant  food ;  Vola- 
tile matter  of  soils  ;  Distribution  of  plant  food  in  the  soil ; 
Composition  of  typical  soils ;  ;  Alkali '  soils  and  their 
improvement ;  Acid  soils  ;  Organic  compounds  of  soil ; 
Sources  ;  Classification ;  Humus  ;  Humates ;  Humifica- 
tion;  Humates  produced  by  different  kinds  of  organic 
matter ;  Mineral  matter  combined  with  humus ;  Value  of 
humates  as  plant  food ;  Amount  of  plant  food  in  humic 
forms ;  Physical  properties  of  soils  influenced  by  humus ; 
Loss  of  humus  by  forest  fires,  by  prairie  fires,  by  cultiva- 
tion ;  Humic  acid ;  Soils  in  need  of  humus  ;  Soils  not  in 
need  of  humus ;  Composition  of  humus  from  old  and  new 
soils ;  Influence  of  different  methods  of  farming  upon 
humus. 

CHAPTER  IV 
[  NITROGEN  OF  THE  SOIL  AND  Am,  NITRIFICATION,  AND  Ni- 

V TROGENOUS   MANURES  ) Il6-I57 

rlmportance  of  nitrOgen  as  plant  food  ;  Atmospheric  ni- 
trogen as  a  source  of  plant  food  A  Experiments  of  Bous- 
singault,  Ville,  Lawes  and  Gilbert,  and  Atwater;  Result 
of  field  trials ;  Experiments  of  Hellriegel  and  Wilfarth 
and  recent  investigators ;  Composition  of  root  nodules ; 
Amount  of  nitrogen  returned  to  soil  by  leguminous  crops 
and  importance  to  agriculture ;  Nitrogenous  compounds 
of  the  soil ;  Origin  ;  Organic  nitrogen  ;  Amount  of  nitro- 
gen in  soils ;  Removed  in  crops ;  Nitrates  and  nitrites ; 
Ammonium  compounds ;  Ammonia  in  rain  and  drain 


CONTENTS 


waters ;  Ratio  of  nitrogen  to  carbon  in  the  soil ;  Losses 
of  nitrogen  from  soils ;  Gains  of  nitrogen  to  soils ;  Nitri- 
fication :  Former  views  regarding ;  Workings  of  an  organ- 
ism ;  Conditions  necessary  for  nitrification;  Influence  of 
cultivation  upon  these  conditions  ;  Nitrous  acid  organisms, 
ammonia-producing  organisms,  denitrification,  number  and 
kind  of  organisms  in  soils ;  Inoculation  of  soils  with 
organisms ;  Chemical  products  produced  by  organisms ; 
Losses  of  nitrogen  by  fallowing  rich  prairie  lands ;  Influ- 
ence of  plowing  upon  nitrification ;  Nitrogenous  manures ; 
Sources ;  Dried  blood,  tankage,  flesh  meal,  fish  scrap, 
seed  residue,  and  uses  of  each  ;  Leather,  wool  waste,  and 
hair ;  Available  organic  nitrogen ;  Peat  and  muck ;  Le- 
guminous crops  as  nitrogenous  fertilizers  ;  Sodium  nitrate, 
ammonium  salts ;  Calcium  cyanamid ;  Cost  and  value  of 
nitrogenous  fertilizers. 

CHAPTER  V 

FARM  MANURES 158-190 

Variable  composition  of  farm  manures ;  Average  com- 
position of  manures  ;  Factors  which  influence  composition 
of  manures ;  Absorbents ;  Use  of  peat  and  muck  as  ab- 
sorbents ;  Relation  of  food  consumed  to  manures  pro- 
duced ;  Bulky  and  concentrated  foods ;  Course  of  the 
nitrogen  of  the  food  during  digestion ;  Composition  of 
liquid  and  solid  excrements ;  Manurial  value  of  foods ; 
Commercial  valuation  of  manure ;  Influence  of  age  and 
kind  of  animal ;  Manure  from  young  and  old  animals ; 
Cow  manure ;  Horse  manure ;  Sheep  manure ;  Hog  ma- 
nure ;  Hen  manure ;  Mixing  manures ;  Volatile  products 
from  manure ;  Human  excrements ;  Preservation  of  ma- 
nures ;  Leaching ;  Losses  by  fermentation  ;  Different  kinds 
of  fermentation ;  Water  necessary  for  fermentation ;  Heat 


CONTENTS  xi 

PAGES 

produced  during  fermentation;  Composting  manures; 
Uses  of  preservatives  ;  Manure  produced  in  sheds  ;  Value 
of  protected  manure ;  Use  of  manures ;  Direct  hauling  to 
field ;  Coarse  manures  injurious  ;  Manuring  pasture  land ; 
Small  piles  of  manure  in  fields  objectionable;  Rate  of 
application ;  Most  suitable  crops  to  apply  to ;  Compara- 
tive value  of  manure  and  food ;  Lasting  effects  of  manure  ; 
Comparative  value  of  good  and  poor  manure ;  Summary 
of  ways  in  which  manures  may  be  beneficial. 

CHAPTER   VI 

FIXATION 191-197 

Fixation  a  chemical  change,  examples  of;  Fixation  and 
absorption ;  Due  to  zeolites  ;  Humus  and  fixation  ;  Soils 
possess  different  powers  of  fixation ;  Nitrates  do  not 
undergo  fixation ;  Fixation  of  potash,  phosphoric  acid, 
and  ammonia;  Fixation  may  make  plant  food  less  avail- 
able ;  Fixation  a  desirable  property  of  soils  ;  Fixation  and 
the  action  of  manures ;  Fixation  and  soil  solution. 

CHAPTER   VII 
[PHOSPHATE  FERTILIZERS)     .        .        .  .        .      198-211 

Importance  of  phosphorus  as  plant  food ;  Amount  re- 
moved in  crops ;  Amount  and  source  of  phosphoric  acid 
in  soils  ;  Commercial  forms  of  phosphoric  acid ;  Phosphate 
rock  ;  Calcium  phosphates ;  Reverted  phosphoric  acid ; 
Available  phosphoric  acid ;  Manufacture  of  phosphate 
fertilizers,  acid  phosphates,  superphosphates ;  Commercial 
value  of  phosphoric  acid ;  Basic  slag  phosphate ;  Guano ; 
Bones  ;  Steamed  bone  ;  Dissolved  bone ;  Bone  black ; 
Fineness  of  division  of  phosphate  fertilizers ;  Use  of 
phosphate  fertilizers ;  How  to  keep  the  phosphoric  acid 
of  the  soil  available. 


Xll  CONTENTS 


x     CHAPTER  VIII 

f~  \  PAGES 

/  POTASH  FERTILIZERS] 212-222 

V  Potassium  an  essential  element ;  Amount  of  potash  re- 

moved in  crops ;  Amount  in  soils  ;  Source  of  soil  potash  ; 
Commercial  forms  of  potash ;  Stassfurt  salts,  occurrence 
of;Kainit;  Muriate  of  potash  ;  Sulphate  of  potash  ;  Other 
Stassfurt  salts;  Wood  ashes,  composition  of;  Amount  of 
ash  in  different  kinds  of  wood  ;  Action  of  ashes  on  soils ; 
Leached  ashes ;  The  alkalinity  of  ashes ;  Coal  ashes ; 
Miscellaneous  ashes ;  Commercial  value  of  potash  ;  Use 
of  potash  fertilizers ;  Joint  use  of  potash  and  lime. 

CHAPTER   IX 

\  LIME  AND  MISCELLANEOUS  FERTILIZERS]    .        .        .     223-232 

Calcium  an  essential  element ;  Am/unt  of  lime  removed 
in  crops ;  Amount  of  lime  in  soils ;  Different  kinds  of 
lime  fertilizers  ;  Their  physical  and  chemical  action ;  Action 
of  lime  upon  organic  matter  and  in  correcting  acidity  of 
soils  ;  Lime  liberates  potash  ;  Aids  nitrification  ;  Action  of 
land  plaster  on  some  '  alkali '  soils  ;  Quicklime  and  slaked 
lime ;  Pulverized  lime  rock ;  Marl ;  Physical  action  of 
lime ;  Judicious  use  of  lime ;  Miscellaneous  fertilizers ; 
Salt  and  its  action  on  the  soil ;  Magnesium  salts ;  Soot ; 
Seaweed ;  Strand  plant  ash ;  Wool  washings ;  Street 
sweepings. 

CHAPTER  X 

/COMMERCIAL  FERTILIZERS  1 233-254 

History  of  development  of  industry ;  Complete  fertili- 
zers and  amendments ;'  Variable  composition  of  commer- 
cial fertilizers ;  Preparation  of  fertilizers ;  Inert  forms  of 


CONTENTS  Xlll 

PAGES 

matter  in  fertilizers  ;  Inspection  of  fertilizers ;  Mechanical 
condition  of  fertilizers ;  Forms  of  nitrogen,  phosphoric 
acid,  and  potash  in  commercial  fertilizers ;  Misleading 
statements  on  fertilizer  bags ;  Estimating  the  value  of  a 
fertilizer ;  Home  mixing ;  Fertilizers  and  tillage ;  Abuse 
of  commercial  fertilizers;  Judicious  use  of;  Field  tests; 
Preliminary  experiments ;  Verifying  results ;  Deficiency 
of  nitrogen,  phosphoric  acid,  potash,  and  of  two  elements ; 
Importance  of  field  trials;  Will  it  pay  to  use  fertilizers? 
Amount  to  use  per  acre ;  Influence  of  excessive  applica- 
tions ;  Fertilizing  special  crops ;  Commercial  fertilizers 
and  farm  manures. 

CHAPTER  XI 

FOOD  REQUIREMENTS  OF  CROPS 255-272 

Amount  of  fertility  removed  by  crops ;  Assimilative 
powers  of  crops  compared ;  (Ways  in  which  plants  obtain 
their  food j  Cereal  crops,  general  food  requirements ; 
Wheat ;  Barley ;  Oats ;  Corn ;  Miscellaneous  crops  ;  Flax ; 
Potatoes  ;  Sugar  beets ;  Roots ;  Turnips ;  Rape  ;  Buck- 
wheat ;  Cotton ;  Hops ;  Hay  and  grass  crops ;  Leguminous 
crops ;  Garden  crops  ;  Fruit  trees ;  Small  fruits ;  Lawns. 

CHAPTER  XII 

ROTATION  OF  CROPS  AND  CONSERVATION   OF   SOIL   FER- 
TILITY          273-290 

Object  of  rotating  crops ;  Principles  involved  in  crop 
rotation  ;  Deep-  and  shallow-rooted  crops  ;  Humus-con- 
suming and  humus-producing  crops ;  Crop  residues  ;  Ni- 
trogen-consuming and  nitrogen-producing  crops  ;  Rotation 
and  mechanical  condition  of  soil ;  Economic  use  of  soil 
water;  Rotation  and  farm  labor;  Economic  use  of  ma- 
nures ;  Salable  crops ;  Rotations  advantageous  in  other 


XIV  CONTENTS 

PAGES 

ways ;  Long-  and  short-course  rotations ;  Example  of 
rotation  ;  Problems  in  rotations  ;  Conservation  of  fertility  ; 
Necessity  of  manures ;  Use  of  crops ;  Two  systems  of 
farming  compared ;  Losses  of  fertility  with  different 
methods  of  farming ;  Problems  on  income  and  outgo  of 
fertility  from  farms. 

CHAPTER  XIII 

PREPARATION  OF  Soi^s  FOR  CROPS      ....      291-306 

Importance  of  good  physical  condition  of  seed  bed ;  In- 
fluence of  methods  of  plowing  upon  the  condition  of  the 
seed  bed ;  Influence  of  moisture  content  of  the  soil  at  the 
time  of  plowing;  Influence  upon  the  seed  bed  of  pulver- 
izing and  fining  the  soil ;  Aeration  of  seed  bed  necessary ; 
Preparation  of  seed  bed  without  plowing  ;  Mixing  of  sub- 
soil with  seed  bed;  Cultivation  to  destroy  weeds;  Influ- 
ence of  cultivation  upon  bacterial  action ;  Cultivation  for 
special  crops ;  Cultivation  to  prevent  washing  and  gully- 
ing of  lands;  Bacterial  diseases  of  soils;  Influence  of 
crowding  of  plants  in  the  seed  bed ;  Selection  of  crops  , 
Inherent  and  cumulative  fertility  of  soils ;  Balanced  soil 
conditions. 

CHAPTER  XIV 

LABORATORY  PRACTICE 307-326 

General  directions ;  Note  book ;  Apparatus  used  in 
work ;  Determination  of  hydroscopic  moisture  of  soils ; 
Determination  of  the  volatile  matter;  Determination  of 
the  capacity  of  loose  soils  to  absorb  water ;  Determination 
of  capillary  water  of  soils  ;  Capillary  action  of  water  upon 
soils;  Influence  of  manure  and  shallow  surface  cultivation 
upon  moisture  content  and  temperature  of  soils ;  Weight 


CONTENTS  XV 

PAGES 

of  soils ;  Influence  of  color  upon  the  temperature  of  soils  ; 
Rate  of  movement  of  air  through  soils ;  Rate  of  move- 
ment of  water  through  soils ;  Separation  of  sand,  silt,  and 
clay;  Sedimentation  of  clay;  Properties  of  rocks  from 
which  soils  are  derived ;  Form  and  size  of  soil  par- 
ticles ;  Pulverized  rock  particles  ;  Reaction  of  soils  ;  The 
granulation  of  soils  ;  Absorption  of  gases  by  soils  ;  Acid 
insoluble  matter  of  soils ;  Acid  soluble  matter  of  soils ; 
Extraction  of  humus  from  soils  ;  Nitrogen  in  soils ;  Test- 
ing for  nitrates  ;  Volatilization  of  ammonium  salts ;  Test- 
ing for  phosphoric  acid  ;  Preparation  of  acid  phosphate ; 
Solubility  of  organic  nitrogenous  compounds  in  pepsin 
solution  ;  Preparation  of  fertilizers  ;  Testing  ashes  ;  Ex- 
tracting water  soluble  materials  from  a  commercial  fertili- 
zer; Influence  of  continuous  cultivation  and  crop  rotation 
upon  the  properties  of  soil ;  Summary  of  results  with  tests 
of  home  soil. 

REVIEW  QUESTIONS 327~339 

REFERENCES  .........      340-344 

INDEX 345-35° 


SOILS  AND  FERTILIZERS 


INTRODUCTION 

PRIOR  to  1800  but  little  was  known  of  the  sources 
and  importance  of  plant  food.  Manures  had  been 
used  from  the  earliest  times,  and  their  value  was  recog- 
nized, although  the  fundamental  principles  underlying 
their  use  were  not  understood.  It  was  believed  they 
acted  in  some  mysterious  way.  The  alchemists  had 
advanced  various  views  regarding  them ;  one  was  that 
the  so-called  "  spirits "  left  the  decaying  manure  and 
entered  the  plant,  producing  more  vigorous  growth. 
As  evidence,  the  worthless  character  of  leached  manure 
was  cited.  It  was  thought  the  spirits  had  left  such 
manure.  The  terms  '  spirits  of  hartshorn,'  '  spirits  of 
niter,'  '  spirits  of  turpentine,'  and  many  others  reflect 
these  ideas  regarding  the  composition  of  matter. 

The  alchemists  held  that  one  substance,  as  copper, 
could  be  changed  to  another  substance,  as  gold.  Plants 
were  supposed  to  be  water  transmuted  in  some  myste- 
rious way  directly  into  plant  tissue.  Van  Helmont,  in 
the  seventeenth  century,  attempted  to  prove  this.  "  He 
took  a  large  earthen  vessel  and  filled  it  with  200 
pounds  of  dried  earth.  In  it  he  planted  a  willow 


2  SOILS     AND     FERTILIZERS 

weighing  5  pounds,  which  he  duly  watered  with  rain 
and  distilled  water.  After  five  years  he  pulled  up  the 
willow  and  it  now  weighed  169  pounds  and  3  ounces."1 
He  concluded  that  164  pounds  of  roots,  bark,  leaves, 
and  branches  had  been  produced  by  direct  transmu- 
tation of  the  water. 

It  is  evident  from  the  preceding  example  that  any- 
thing like  an  adequate  idea  of  the  growth  and  compo- 
sition of  plant  bodies  could  not  be  gained  until  the 
composition  of  air  and  water  was  established. 

The  discovery  of  oxygen  by  Priestley  in  1774,  of 
the  composition  of  water  by  Cavendish  in  1781,  and 
of  the  r61e  which  carbon  dioxide  plays  in  plant  and 
animal  life  by  DeSaussure  and  others  in  1800,  formed 
the  nucleus  of  our  present  knowledge  regarding  the 
sources  of  matter  stored  up  in  plants.  It  was  between 
1760  and  1800  that  alchemy  lost  its  grip  because  of 
advances  in  knowledge  and  the  way  was  opened  for 
the  development  of  modern  chemistry. 

)e  Saussure's  "  Recherches  sur  la  Ve'ge'tation,"  pub- 
lished in  1804,  was  the  first  systematic  work  showing 
the  sources  of  the  compounds  stored  up  in  plant  bodies. 
He  demonstrated,  quantitatively,  that  the  increase  in  the 
amount  of  carbon,  hydrogen,  and  oxygen,  when  plants 
were  exposed  to  sunlight,  was  at  the  expense  of  the 
carbon  dioxide  of  the  air,  and  of  the  water  of  the  soil. 
He  also  maintained  that  the  mineral  elements  derived 
from  the  soil  were  essential  for  plant  growth,  and  gave 
the  results  of  the  analyses  of  many  plant  ashes.  He 


INTRODUCTION  3 

believed  that  the  nitrogen  of  the  soil  was  the  main 
source  of  the  nitrogen  found  in  plants.  These  views 
have  since  been  verified  by  many  investigators,  and  are 
substantially  those  held  at  the  present  time  regarding 
the  fundamental  principles  of  plant  growth.  They  were 
not,  however,  accepted  as  conclusive  at  the  time,  and  it 
was  not  until  nearly  a  half-century  later,  when  Bous- 
singault,  Liebig,  and  others  repeated  the  investigations 
of  De  Saussure,  that  they  were  finally  accepted  by  chem- 
ists and  botanists. 

From  the  time  of  De  Saussure  to  1835,  scientific 
experiments  relating  to  plant  growth  were  not  actively 
prosecuted,  but  the  facts  which  had  accumulated  were 
studied,  and  attempts  were  made  to  apply  the  results 
to  actual  practice.  Among  the  first  to  see  the  relation 
between  chemistry  and  agriculture  was  Sir  Humphry 
Davy.  In  1813  he  published  his  "Essentials  of  Agri- 
cultural Chemistry,"  which  treated  of  the  composition 
of  air,  soil,  manures,  and  plants,  and  of  the  influence 
of  light  and  heat  upon  plant  growth.  About  this 
period,  Thaer  published  an  important  work  entitled 
"  Principes  Raisonnes  d' Agriculture."  He  believed 
humus  determined  the  fertility  of  the  soil,  that  plants 
obtained  their  food  mainly  from  humus,  and  that  the 
carbon  compounds  of  plants  were  produced  from  the 
organic  carbon  compounds  of  the  soil.  This  gave  rise 
to  the  so-called  humus  theory,  which  was  later  shown 
to  be  an  inadequate  idea  regarding  the  source  of  plant 
food,  and  for  a  time  it  prevented  the  actual  value  of 


4  SOILS    AND    FERTILIZERS 

humus  as  a  factor  of  soil  fertility  from  being  recog- 
nized. The  writings  of  Thaer  were  of  a  most  prac- 
tical nature,  and  they  did  much  to  stimulate  later 
investigations. 

About  1830  there  was  renewed  interest  in  scientific 
investigations  relating  to  agriculture.  At  this  time 
Boussingault,  a  French  investigator,  became  actively 
engaged  in  agricultural  research.  He  was  the  first  to 
have  a  chemical  laboratory  upon  a  farm  and  to  make 
practical  investigations  in  connection  with  agriculture. 
This  marks  the  establishment  of  the  first  agricultural 
experiment  station.  Boussingault's  work  upon  the  as- 
similation of  the  free  nitrogen  of  the  air  is  reviewed  in 
Chapter  IV.  His  study  of  the  rotation  of  crops  was 
a  valuable  contribution  to  agricultural  science.  He  dis- 
covered many  important  facts  relating  to  the  chemical 
characteristics  of  foods,  and  was  the  first  to  make  a 
comparison  as  to  the  amount  of  nitrogen  in  differ- 
ent kinds  of  foods  and  to  determine  their  value  on  the 
basis  of  the  nitrogen  content.  His  study  of  the  pro- 
duction of  saltpeter  did  much  to  prepare  the  way  for 
later  work  on  nitrification.  The  investigations  of  Bous- 
singault covered  a  variety  of  subjects  relating  to  plant 
growth.  He  repeated  and  verified  much  of  the  earlier 
work  of  De  Saussure,  and  also  secured  many  additional 
facts  regarding  the  chemistry  of  growth.  As  to  the 
source  of  nitrogen  in  crops,  he  states :  "  The  soil  fur- 
nishes the  crops  with  mineral  alkaline  substances,  pro- 
vides them  with  nitrogen,  by  ammonia  and  by  nitrates, 


INTRODUCTION  5 

which  are  formed  in  the  soil  at  the  expense  of  the  nitrog- 
enous matter  contained  in  diluvium,  which  is  the  basis 
of  vegetable  earth ;  compounds  in  which  nitrogen  exists 
in  stable  combination,  only  becoming  fertilizing  by  the 
effect  of  time."  As  to  the  absorption  of  the  gaseous 
nitrogen  of  the  air  by  vegetable  earth,  he  says  :  "  I  am 
not  acquainted  with  a  single  irreproachable  observation 
that  establishes  it ;  not  only  does  the  earth  not  absorb 
gaseous  nitrogen,  but  it  gives  it  off."  2 

The  investigations  of  DeSaussure  and  Boussingault, 
and  the  writings  of  Davy,  Thaer,  Sprengel,  and  Schiib- 
ler  prepared  the  way  for  the  work  and  writings  of  Lie- 
big.  In  1840  he  published  "Organic  Chemistry  in  its 
Applications  to  Agriculture  and  Physiology."  Liebig's 
agricultural  investigations  were  preceded  by  many  valu- 
able discoveries  in  organic  chemistry,  which  he  applied 
directly  in  his  interpretations  of  agricultural  problems. 
His  writings  were  of  a  forceful  character  and  were  ex- 
tremely argumentative.  They  provoked,  as  he  intended, 
vigorous  discussions  upon  agricultural  problems.  He 
assailed  the  humus  theory  of  Thaer,  and  showed  that 
humus  was  not  an  adequate  source  of  the  plant's  carbon. 
In  the  first  edition  of  his  work  he  noted  that  farms 
from  which  certain  products  were  sold  became  less  pro- 
ductive, because  of  the  loss  of  nitrogen.  In  a  second 
edition  he  considered  that  the  combined  nitrogen  of 
the  air  was  sufficient  for  crop  production.  He  overesti- 
mated the  amount  of  ammonia  in  the  air,  and  underesti- 
mated the  value  of  the  nitrogen  in  soils  and  manures. 


6  SOILS    AND     FERTILIZERS 

A  study  of  the  composition  of  ash  of  plants  led  him 
to  propose  the  mineral  theory  of  plant  nutrition. 
De  Saussure  had  shown  that  plants  contain  certain  min- 
eral elements,  but  he  did  not  emphasize  their  impor- 
tance as  plant  food.  Liebig's  writings  on  the  composi- 
tion of  plant  ash,  and  his  emphasizing  the  importance  of 
supplying  crops  with  mineral  food,  led  to  the  commer- 
cial preparation  of  manures,  which  in  later  years  devel- 
oped into  the  commercial  fertilizer  industry.  The  work 
of  Liebig  was  not  conducted  in  connection  with  field 
experiments.  It  had,  however,  a  most  stimulating  in- 
fluence upon  investigations  in  agricultural  chemistry, 
and  to  him  we  owe,  in  a  great  degree,  the  summarizing 
of  previous  disconnected  work  and  the  mapping  out  of 
valuable  lines  for  future  investigations. 

Liebig's  enthusiasm  for  agricultural  investigations 
may  be  judged  from  the  following  extract :  "  I  shall  be 
happy  if  I  succeed  in  attracting  the  attention  of  men 
of  science  to  subjects  which  so  well  merit  to  engage 
their  talents  and  energies.  Perfect  agriculture  is  the 
true  foundation  of  trade  and  industry  ;  it  is  the  founda- 
tion of  the  riches  of  states.  But  a  rational  system  of 
agriculture  cannot  be  formed  without  the  application  of 
scientific  principles,  for  such  a  system  must  be  based  on 
an  exact  acquaintance  with  the  means  of  nutrition  of 
vegetables,  and  with  the  influence  of  soils,  and  actions 
of  manures  upon  them.  This  knowledge  we  must  seek 
from  chemistry,  which  teaches  the  mode  of  investigat- 
ing the  composition  and  of  the  study  of  the  character  of 


INTRODUCTION  7 

the  different  substances  from  which  plants  derive  their 
nourishment."3 

Soon  after  Liebig's  first  work  appeared,  the  investi- 
gations at  Rothamsted  by  Sir  J.  B.  Lawes  were  under- 
taken. The  most  extensive  systematic  work  in  both 
field  experiments  and  laboratory  investigations  ever 
conducted  has  been  carried  on  by  Lawes  and  Gilbert 
at  Rothamsted,  Eng.  Dr.  Gilbert  had  previously  been 
a  pupil  of  Liebig,  and  his  becoming  associated  with 
Sir  J.  B.  Lawes  marks  the  establishment  of  the  second 
experiment  station.  Many  of  the  Rothamsted  experi- 
ments have  been  continued  since  1844,  and  results  of 
the  greatest  value  to  agriculture  have  been  obtained. 
The  investigations  on  the  non-assimilation  of  atmos- 
pheric nitrogen  by  crops,  published  in  1861,  were  ac- 
cepted as  conclusive  evidence  upon  this  much-vexed 
question.  Their  work  on  manures,  nitrification,  the 
nitrogen  supply  of  crops,  and  the  increase  and  decrease 
of  the  nitrogen  of  the  soil  when  different  crops  are  pro- 
duced, has  had  a  most  important  bearing  upon  main- 
taining the  fertility  of  soils. 

"  The  general  plan  of  the  field  experiments  has  been 
to  grow  some  of  the  most  important  crops  of  rotation, 
each  separately,  for  many  years  in  succession  on  the 
same  land,  without  manure,  with  farmyard  manure, 
and  with  a  great  variety  of  chemical  manures,  the 
same  kind  of  manure  being,  as  a  rule,  applied  year 
after  year  on  the  same  plot.  Experiments  with  differ- 
ent manures  on  the  mixed  herbage  of  permanent  grass 


8  SOILS    AND    FERTILIZERS 

land,  on  the  effects  of  fallow,  and  on  the  actual  course 
of  rotation  without  manure,  and  with  different  manures 
have  likewise  been  made."4 

In  addition  to  Davy,  Thaer,  De  Saussure,  Boussin- 
gault,  Liebig,  and  Lawes  and  Gilbert,  a  great  many 
others  have  contributed  to  our  knowledge  of  the  prop- 
erties of  soils.  The  work  of  Pasteur,  while  it  did  not 
directly  relate  to  soils,  indirectly  had  great  influence 
upon  soil  investigations.  His  researches  upon  fermen- 
tation made  it  possible  for  Schlosing  to  prove  that 
nitrification  is  the  result  of  the  workings  of  living 
organisms.  These  have  since  been  isolated  and  studied 
by  Warington  and  Winogradsky. 

The  importance  of  the  physical  condition  of  the  soil 
and  its  relation  to  crop  production  was  recognized  by 
agriculturists  at  about  the  same  time  that  the  sources 
of  plant  food  were  being  investigated.  Jethro  Tull 
published  in  1829  a  work  entitled  "The  Horse-Hoeing 
Husbandry,"  which  emphasized  the  importance  of 
thorough  cultivation  of  the  soil.  That  increase  in  the 
yield  of  crops,  destruction  of  weeds,  reduction  of  rust 
and  blight  of  wheat,  and  general  improvement  of  the 
soil,  are  all  results  of  improved  tillage  is  clearly  set 
forth  in  Tull's  work.  Tull  was  inclined  to  believe  that 
tillage  could  take  the  place  of  manure.  "  All  sorts  of 
dung  and  compost  contain  some  matter  which,  when 
mixed  with  the  soil,  ferments  therein ;  and  by  such  fer- 
ment dissolves,  crumbles,  and  divides  the  earth  very 
much.  This  is  the  chief  and  almost  only  use  of  dung." 


INTRODUCTION  9 

While  underestimating  the  value  of  manure,  he  has 
shown  the  importance  of  thorough  tillage  of  the  soil 
more  clearly  than  had  ever  been  done  before.  "The 
Horse-Hoeing  Husbandry "  by  Jethro  Tull  is  worthy 
of  careful  study  by  all  agricultural  students. 

During  recent  years  the  agricultural  experiment 
stations  of  this  and  other  countries  have  made  soils  a 
prominent  feature  of  their  work.  Some  of  the  results 
obtained  are  noted  in  the  following  chapters.  Our 
knowledge  regarding  the  chemistry,  physics,  geology, 
and  bacteriology  of  soils  is  still  far  from  complete, 
but  many  facts  have  been  discovered  which  are  of  the 
greatest  value  to  the  practical  farmer.  The  literature 
relating  to  soils  and  fertilizers  has  become  very  exten- 
sive, and  in  the  classification  of  agricultural  subjects 
for  study,  the  soil  forms  one  of  the  main  divisions  of 
agronomy. 

In  soil  investigations  it  has  frequently  happened, 
owing  to  imperfect  interpretation  of  results  and  to 
the  presence  of  many  modifying  influences,  that  the 
conclusions  of  one  investigator  appear  to  be  directly 
contradictory  to  those  of  another.  This  is  well  illus- 
trated in  the  investigations  relating  to  the  assimilation 
of  free  atmospheric  nitrogen,  where  seemingly  opposite 
conclusions  now  form  a  complete  theory. 

A  scientific  study  of  soils  is  valuable  from  an  educa- 
tional point  of  view,  as  well  as  because  the  practical 
knowledge  obtained  can  be  utilized  in  the  production 
of  crops.  In  the  cultivation  of  soils,  complicated  physi- 


IO  SOILS     AND     FERTILIZERS 

cal,  bacteriological,  and  chemical  changes  occur,  many 
of  which  are  only  imperfectly  understood.  The  fun- 
damental principles  of  soil  fertility  are,  however,  rea- 
sonably well  established,  and  it  is  now  possible  to 
intelligently  conserve  the  fertility  of  soils  and  to  pro- 
duce maximum  yields  of  crops.  Since  the  soil  wealth 
is  the  greatest  and  the  most  important  form  of  wealth 
of  a  nation,  intelligent  effort  should  be  made  for  its 
conservation  and  development. 


CHAPTER   I 
PHYSICAL   PROPERTIES   OF   SOILS 

1.  Soil.  —  Soil  is  that  portion  of  the  earth's  crust 
in  which  plants  may  grow.  It  is  composed  of  pulver- 
ized and  disintegrated  rock  mixed  with  animal  and 
vegetable  matter.  The  rock  particles  are  of  different 
kinds  and  sizes,  and  are  in  various  stages  of  decomposi- 
tion. If  two  soils  are  produced  from  the  same  kind  of 
rock  and  differ  only  in  the  size  of  the  particles,  the 
difference  is  merely  a  physical  one.  If,  however,  one 
soil  is  formed  largely  from  sandstone,  while  the  other  is 
formed  from  granite,  and  the  soil  particles  are  not  the 
same  in  size,  the  difference  is  both  physical  and  chemi- 
cal. Soils  are  derived  from  different  kinds  of  rock 
fragments,  which  are  composed  of  minerals  having 
a  different  combination  of  elements  and  different  per- 
centage composition,  and  hence  it  is  they  differ  both 
physically  and  chemically.  It  is  difficult  to  consider 
the  physical  properties  without  also  considering  the 
chemical  properties.  The  chemical  and  physical  prop- 
erties, together,  determine  largely  the  agricultural  value 
of  a  soil. 

ii 


12  SOILS   AND    FERTILIZERS 

2.  Physical  Properties  Defined.  —  The  physical  prop- 
erties of  a  soil  are  : 

1.  Weight  and  volume. 

2.  Size,  form,  and  arrangement  of  the  soil  particles. 

3.  The  relation  of  the  soil  to  air,  water,  heat,  and 
cold. 

4.  Color. 

5.  Odor  and  taste. 

6.  The  relation  of  the  soil  to  electricity. 

3.  Weight  and  Volume.  —  Soils  vary  in  weight  with  the 
composition  and  size  of  the  particles.  Fine  sandy  soils 
weigh  heaviest,  while  peaty  soils  are  the  lightest. 
But  when  saturated  with  water,  a  cubic  foot  of  peaty 
soil  weighs  more  than  a  cubic  foot  of  sandy  soil.  A 
given  volume  of  clay  soil  weighs  less  than  the  same 
volume  of  sandy  soil.  The  larger  the  amount  of  or- 
ganic matter,  the  less  the  weight.  Pasture  land,  for 
example,  weighs  less  than  arable  land.  A  cubic  foot 
of  soil  from  a  field  which  has  been  well  cultivated 
weighs  less  than  that  from  a  field  where  the  soil  has 
been  compacted.  Weight  is  an  important  property  to 
consider  when  the  total  amounts  of  plant  food  in  two 
soils  are  compared.  A  peaty  soil  containing  i  per  cent 
of  nitrogen  and  weighing  30  pounds  per  cubic  foot  has 
less  total  nitrogen  than  a  soil  containing  0.40  per  cent 
of  nitrogen  and  weighing  80  pounds. 

The  weight  of  soils  per  cubic  foot  as  determined  from 
apparent  density  is  approximately  as  follows : 5 


PHYSICAL    PROPERTIES    OF    SOILS  13 


POUNDS 

7O  to  7S 

95  to  i  10 

7C  to  QO 

2  C  to  4O 

Average  prairie  soil     

7C 

6; 

It  is  estimated  that  an  acre  of  soil  to  the  depth  of 
one  foot  weighs  in  round  numbers  from  2,500,000  to 
4,200,000  pounds,  depending  upon  the  chemical  com- 
position, size  of  soil  particles,  and  state  of  compac- 
tion. 

The  weight  per  cubic  foot  of  soils  in  situ  generally 
exceeds  the  weight  derived  from  the  apparent  density 
of  the  dry  soil ;  this  is  because  of  the  tendency  of  soils 
in  the  field  to  become  compacted.  While  a  dry  clay 
soil  reduced  to  a  powder  may  show  an  apparent  weight 
of  70  pounds  per  cubic  foot,  the  field  weight  (air-dry 
basis)  may  range  from  80  to  98  pounds,  depending  upon 
the  degree  of  compactness. 

Between  the  soil  particles  are  non-capillary  or  pore 
spaces  occupied  by  air  or  water.  If  the  soil  be  con- 
sidered a  homogeneous  mass  without  air  spaces,  it  will 
have  an  absolute  specific  gravity  of  about  2.6 ;  with  the 
air  spaces  its  apparent  specific  gravity  is  about  1.2. 
That  is,  in  its  natural  condition  a  soil  weighs  about  1.2 
times  heavier  than  the  same  volume  of  water.  The 
porosity  of  a  soil  is  determined  by  dividing  the  apparent 


SOILS     AND     FERTILIZERS 


by  the  real  specific  gravity.6  Ordinarily  cultivated  soils 
have  a  pore  space  range  from  30  to  60  per  cent  of  the 
volume  of  the  soil,  depending  upon  the  conditions  to 
which  the  soil  has  been  subjected. 

4.  Size  of  Soil  Particles.  —  The  size  of  soil  particles 
varies  from  those  hardly  distinguishable  with  the  micro- 
scope to  coarse  rock  fragments  and  determines  the  type 
of  a  soil  as  sand,  clay,  or  loam.  The  term  '  fine  earth  ' 
is  used  to  designate  that  part  of  a  soil  which  passes 
through  a  sieve  with  holes  0.5  mm.  (0.02  inch)  in  di- 
ameter. Coarse  sand  particles  and  rock  fragments 
which  fail  to  pass  through  the  sieve  are  called  skeleton. 
The  amounts  of  fine  earth  and  skeleton  are  variable. 
Arable  soils,  in  general,  contain  from  5  to  20  per  cent 
of  skeleton. 

The  fine  earth  is  composed  of  six  grades  of  soil  parti- 
cles. The  names  and  sizes  are  as  follows : 


MILLIMETERS 

INCHES 

Medium  sund          

0.5  to  0.25 

O.O2  to  O.OI 

Fine  sand     ....... 

0.25  to  o.i 

o.oi  to  0.004 

o.i  to  0.05 

O.OO4  to  O.OO2 

Silt      

0.05  to  o.oi 

O.OO2  to  O.OOO4 

Fine  silt  

o.oi  to  0.005 

O.OOO4  tO  O.OOO2 

Clay    

0.005  an(^  less 

0.0002  and  less 

Soils  are  mechanical  mixtures  of   various-sized  par- 
ticles.    In  most  soils  there  is  a  predominance  of  one 


PHYSICAL     PROPERTIES     OF     SOILS  1 5 

grade,  as  clay  in  heavy  clay  soils,  and  medium  sand 
in  sandy  soils.  No  soil,  however,  is  composed  entirely 
of  one  grade.  The  clay  particles  are  exceedingly 
small ;  it  would  take  5000  of  the  larger  ones,  if  laid  in 


FIG.  i.  Medium  sand  X  150.  FlG.  2.  Fine  sand  X  150.  FIG.  3.  Very  fine 
sand  x  150.  FIG.  4.  Silt  x  325.  FIG.  5.  Fine  silt  x  325.  FIG.  6.  Clay  x  325. 

a  line  with  the  edges  touching,  to  measure  an  inch, 
while  it  would  take  but  50  of  the  medium  sand  par- 
ticles to  measure  an  inch. 

5.    Sand.  —  Sand  is  any  rock  fragment  ranging  in  size 
between   0.5    and   0.05    mm.   in   diameter.     There  are 


1 6  SOILS    AND    FERTILIZERS 

three  grades,  —  fine,  medium,  and  very  fine.  The  chief 
characteristic  of  sand  is  non-cohesion  of  particles.  A 
soil  composed  entirely  of  sand  has  little,  if  any,  agri- 
cultural value.  Sandy  soils  usually  contain  from  5 
to  15  per  cent  of  clay  and  silt.  The  relative  size  of 
sand,  silt,  and  clay  is  shown  in  the  illustration.  In  the 
coarser  grained  sand,  quartz  predominates,  while  the 
finer  grained  is  composed  mainly  of  other  minerals. 

6.  Clay.  —  The  term  '  clay  '  used  physically  denotes 
those  soil  particles  less  than  0.005  mm-  (0.0002  inch) 
in  diameter,  without  regard  to  chemical  composition. 
It  may  be  silica,  feldspar,  limestone,  mica,  kaolin,  or 
any  other  rock  or  mineral  which  has  been  pulverized 
until  the  particles  are  less  than  0.005  mm-  m  diameter. 
Chemically,  however,  the  term  '  clay '  is  restricted  to  one 
material,  as  explained  in  Section  74.  The  physical 
properties  of  clay  are  well  known.  It  has  the  power  to 
absorb  large  amounts  of  water,  and  will  remain  sus- 
pended in  water  for  a  long  time.  The  roiled  appear- 
ance of  many  streams  and  lakes  is  due  to  the  presence 
of  suspended  clay  particles.  The  amount  in  agricul- 
tural soils  may  range  from  3  to  40  per  cent.  Clay 
soils,  if  worked  when  too  wet,  become  puddled;  then 
percolation  cannot  take  place,  and  the  accumulated 
surface  water  must  be  removed  by  the  slow  process  of 
evaporation.  As  clays  dry,  they  shrink,  become  tena- 
cious, and  are  worked  with  difficulty.  Clay  soils  owe 
their  properties  to  the  fineness  of  division  of  the  par- 


PHYSICAL    PROPERTIES    OF     SOILS  I/ 

tides  rather  than  to  their  chemical  composition.  Any 
mineral  when  finely  pulverized  has  physical  properties 
similar  to  clay.7 

7.  Silt.  —  Silt  is  composed  of  a  great  variety  of  rock 
fragments.  The  particles  are,  in  size,  between  sand 
and  clay.  Chemical  analysis  shows  them  to  be  more 
hydrated  than  the  clay  particles.  Many  of  the  western 
prairie  subsoils,  clay-like  in  nature,  are  composed 
mainly  of  silt,  which  imparts  characteristics  intermedi- 
ate to  sand  and  clay.  While  a  clay  soil  is  nearly  im- 
pervious to  water,  and  when  wet  works  with  difficulty,  a 
silt  soil  is  more  permeable,  but  is  not  so  open  and 
porous  as  a  sandy  soil.  When  a  soil  containing  large 
amounts  of  clay  and  silt  is  treated  with  water,  the  silt 
settles  slowly,  while  the  clay  remains  in  suspension. 
The  fine  deposit  in  ditches  and  drains,  where  the 
water  moves  slowly,  is  mainly  silt.  Soils  composed 
largely  of  silt  deposited  by  water  and  mixed  with  vege- 
table matter  are  among  the  most  fertile. 

8.  Form  of  Soil  Particles.  —  Soil  particles  are  ex- 
tremely varied  in  form.  When  examined  with  the 
microscope  they  show  the  same  diversity  as  is  observed 
among  larger  stones.  In  some  soils  the  particles  are 
spherical,  while  in  others  they  are  angular.  The  shape 
is  determined  by  the  way  in  which  the  soil  has  been 
formed,  and  also  by  the  nature  of  the  rock  from  which 
it  was  produced. 


1 8  SOILS    AND    FERTILIZERS 

The  form  and  arrangement  of  the  particles  are  im- 
portant factors  to  consider  in  dealing  with  the  water 
content  of  soils.  In  the  wheat  lands  of  the  Red  River 
Valley  of  the  North,  the  particles  are  small  and  spher- 
ical, being  formed  largely  from  limestone  rock,  while 
the  subsoil  of  the  western  prairie  regions  is  composed 
largely  of  angular  silt  particles,  intermingled  with  clay, 
forming  a  mass  containing  only  a  minimum  of  inter-soil 
spaces.  The  silt  particles  being  angular  and  embedded 
in  the  clay,  the  soil  has  more  the  character  of  clay  than 
of  silt.  While  these  two  soils  are  unlike  in  physical 
composition,  the  form  and  arrangement  of  the  particles 
give  each  nearly  the  same  water-holding  power.  Two 
soils  may  have  a  somewhat  similar  mechanical  composi- 
tion and  yet  possess  materially  different  physical  proper- 
ties because  of  a  difference  in  the  form  and  arrangement 
of  the  soil  particles.  In  some  soils  10  per  cent  of  clay 
is  of  more  agricultural  value  than  in  other  soils.  Ten 
per  cent  of  clay  associated  with  60  or  70  per  cent  of 
silt  makes  a  good  grain  soil,  while  10  per  cent  of  clay 
associated  largely  with  sand  makes  a  soil  poorly  suited 
to  grain  culture. 

The  classification  of  the  soil  particles  into  clay,  silt, 
and  fine,  medium,  and  coarse  sand  is  purely  an  arbitrary 
one.  Various  authors  use  these  terms  in  different  ways, 
and  when  comparing  the  mechanical  composition  of  soils 
reported  in  different  works,  one  may  avoid  confusion 
by  omitting  the  names  and  noting  only  the  sizes  of  the 
particles. 


PHYSICAL    PROPERTIES    OF    SOILS  1 9 

9.  Number  of  Particles  per  Gram  of  Soil.  —  It  has 
been  estimated  that  a  gram  of  productive  soil  contains 
from  2,000,000,000  to  20,000,000,000  soil  particles  ;  soils 
which  contain  less  than  1,700,000,000  are  unproduc- 
tive. The  number  of  particles  in  a  given  volume  of 
soil  varies  with  their  size  and  form.  According  to 
Whitney8  the  number  of  particles  per  gram  of  differ 
ent  soil  types  is  as  follows  : 

Early  truck 1,955,000,000* 

Truck  and  small  fruit 3,955,000,000 

Tobacco 6,786,000,000 

Wheat 10,228,000,000 

Grass  and  wheat 14,735,000,000 

Limestone 19,638,000,000 

Assuming  the  particles  are  all  spheres,  it  is  es- 
timated that  in  a  cubic  foot  of  soil  a  surface  area  of 
from  two  to  three  and  one  half  acres  is  presented  to 
the  action  of  plant  roots. 

10.   Method  employed  in  Separating  Soil  Particles. — 

Sieves  with  circular  holes  0.5,  0.25,  and  o. I  mm.  are 
employed  for  the  purpose  of  separating  the  coarser 
grades  of  sand.  The  sieve  a,  0.5  mm.  size,  is  connected 
with  the  filtering  flask  c  by  means  of  the  tube  b,  and  the 
flask  is  connected  at  point  d  with  a  suction  pump.  Ten 
grams  of  soil,  after  soft  pestling  with  boiling  water,  are 
placed  in  the  sieve  and  water  is  passed  through  until  the 
washings  are  clear.  All  particles  larger  than  0.5  mm. 
*  Figures  below  sixth  place  omitted  and  ciphers  substituted. 


20 


SOILS    AND    FERTILIZERS 


remain  in  the  sieve,  and  after  drying  and  igniting,  are 
weighed.  The  contents  of  the  flask  c,  containing  the 
particles  less  than  0.5  mm.,  are  now  passed  through  a 
sieve  having  holes  0.25  mm.  in  diameter. 

The  fine  sand  and  silt  are  separated  by  gravity.  The 
fine  sand  with  some  silt  and  clay  are  read- 
ily deposited  and  the  water  containing  the 
suspended  clay  is  decanted  into  a  second 
glass  vessel.  The  residue  is  treated  with 
more  water  and  allowed  to  settle,  this  opera- 
tion being  repeated  until  the  microscope 
shows  the  soil  particles  to  be  nearly  all 
of  one  grade.  The  separation  of  silt 
and  clay  is  facilitated 
by  the  use  of  a  centri- 
fuge.9 

It  is  often  difficult  to 
secure  even  an  approximate  separation  of  sand,  silt,  and 
clay  particles,  because  the  finer  particles  tenaciously  ad- 
here to  the  larger  ones. 

The  clay  is  obtained  by  evaporating  an  aliquot  por- 
tion of  the  washings  or  by  determining  the  total  per 
cent  of  the  other  grades  of  particles  and  the  volatile 
matter  and -subtracting  the  sum  from  100.  This  is  the 
modified  Osborne  sedimentation  method.10 

By  means  of  Hilgard's  elutriator7  a  more  extended  sep- 
aration of  the  soil  particles  is  effected.  For  detailed  direc- 
tions for  making  mechanical  analyses  of  soils  the  student 
is  referred  to  Wiley's  "  Agricultural  Analysis,"  Vol.  I. 


FIG.  7. 


FIG.  8. 


*  ->JV.  -• 


*>       *  <*  *r    *  v- 

**x»  •.  •*      -i^ 

%fjtf^^  «% 


^*;-^-^%y 


I'ine  Silt  Subboil  x  no. 


Silt  Subsoil  x  no. 


*  *  ^    *    -*JVP      j 

ilt  and  Clav  Subsoil  x  no 


•^-^^^ 
J^'*  -  -^V 

i  Hsn*& 

tfssC/^i8-'' 


Sandy  Soil  x  30. 


Sandy  Subsoil  X  30. 


FIG.  9. 


Sand,  clay,  silt,  and  humus  particles 
blended  in  soil  x  no. 


PHYSICAL     PROPERTIES     OF     SOILS 


21 


SOIL  TYPES 

11.  Crop  Growth  and  Physical  Properties.  —  The  pref- 
erence of  certain  crops  for  particular  kinds  of  soil,  as 
wheat  for  a  clay  subsoil,  potatoes  for  a  sandy  soil,  and 
corn  for  a  silt  soil,  is  due  mainly  to  the  characteristic  of 
the  crop  in  requiring  a  definite  amount  of  water,  and  a 
certain  temperature 
for  growth.  These 
conditions  are  met 
by  the  soil  being 
composed  of  various 
grades  of  particles 
which  enable  a  cer- 
tain amount  of  water 
to  be  retained,  and 
the  soil  to  properly 
respond  to  heat  and 
cold.  In  considering 
soil  types,  it  should 
be  remembered  that 
there  are  so  many 
conditions  influenc- 
ing crop  growth  that  FIG.  10.  First  Centrifuge  used  in  the  Mechan- 


the      crop-producing 


ical  Analysis  of  Soils. 

power  cannot  always  be  determined  by  a  mechanical 
analysis  of  the  soil.  The  following  types  have  been 
found  to  hold  true  in  a  large  number  of  cases  under 
average  conditions,  but  they  do  not  represent  what 


22  SOILS    AND    FERTILIZERS 

might  be  true  under  special  conditions.  For  example, 
a  sandy  soil  of  good  fertility  in  which  the  bottom  water 
is  only  a  few  feet  from  the  surface,  may  produce  larger 
grain  crops  than  a  clay  soil  in  which  the  bottom  water 
is  at  a  greater  depth.  In  judging  the  character  of  a 
soil,  the  special  conditions  must  always  be  taken  into 
consideration.  In  discussing  the  following  soil  types,  a 
normal  supply  of  plant  food  and  an  average  rainfall 
are  assumed  in  all  cases.11 

12.  Potato  and  Early  Truck  Soils.  —  The  better  types 
of  potato  soils  are  those  which  contain  about  60  per 
cent  of  medium  and  fine  sand,  30  per  cent  of  silt,  and 
about  5  per  cent  of  clay.  Soils  of  this  nature  when 
supplied  with  3  per  cent  of  organic  matter  will  contain 
from  10  to  20  per  cent  of  water.  The  best  conditions 
for  crop  growth  exist  when  the  soil  contains  about  18 
per  cent  of  water.  In  a  sandy  soil,  vegetation  may 
reduce  the  water  to  a  much  lower  point  than  in  a  clay 
soil,  because  the  sandy  soil  gives  up  its  water  so  readily 
to  growing  crops  and  consequently  a  larger  amount  is 
available,  while  on  a  heavy  clay,  crops  show  the  want  of 
water  when  the  soil  contains  from  10  to  12  per  cent, 
for  the  clay  holds  the  water  so  tenaciously.  When 
potatoes  are  grown  on  soils  where  there  is  an  abnormal 
amount  of  water  the  crop  is  slow  in  maturing.  For 
early  truck  purposes  in  northern  latitudes,  sandy  loam 
soils  are  the  most  suitable  because  they  warm  up  so 
readily,  and  the  absence  of  an  abnormal  amount  of 


PHYSICAL     PROPERTIES     OF     SOILS  23 

water  results  in  early  maturity.  Excellent  crops  of 
potatoes  are  grown  on  many  of  the  silt  soils  of  the 
west  which  have  a  materially  different  composition  from 
the  type  given.  A  soil  may  have  all  of  the  requisites 
physically  for  the  production  of  good  potato  and 
truck  crops,  and  still  be  unproductive  on  account  of 
unbalanced  chemical  composition  or  lack  of  plant 
food. 

13.  General  Truck  and  Fruit  Soils.  —  For  fruit  grow- 
ing and  general  truck  purposes  the  soil  should  contain 
more  clay  and  less  sand  than  for  early  truck  farming. 
Soils  containing  from  10  to  15  per  cent  of  clay  and  not 
more  than  50  per  cent  of  sand  are  best  suited  for  grow- 
ing small  fruits.     Such  soils  will  retain  from  12  to  20 
per  cent  of  water.     There  is  a  noticeable  difference  in 
the  adaptability  of  different  kinds  of  fruit  to  different 
soils.     Some  thrive  on  clay  land,  provided  the  proper 
cultivation  and  treatment  are  given.     There  is  as  much 
diversity  of  soil  required  for  producing  different  fruit 
crops  as  for  the  production  of  different  farm  crops.     As 
a  rule,  however,  a  silt  soil  is  most  capable  of   being 
adapted    to   the   various   conditions   required   by  fruit 
crops. 

14.  Corn  Soils.  —  The  strongest  types  of  corn  soils 
are   those   which   contain  from  40  to  45   per  cent  of 
medium  and  fine  sand  and  about  15  per  cent  of  clay. 
Corn  lands  should   contain    15    per   cent  of  available 


24  SOILS     AND     FERTILIZERS 

water.  Heavy  clays  require  more  cultivation  and  pro- 
duce corn  which  matures  later  than  that  grown  on  soil 
not  so  close  in  texture.  Many  corn  soils  contain  less 
sand  and  clay,  but  more  silt  than  the  figures  given. 
If  a  soil  has  a  high  per  cent  of  neutral  organic  matter, 
good  corn  crops  may  be  produced  where  there  is  less 
than  12  per  cent  of  clay.  Soils  with  a  high  per  cent 
of  sand  are  usually  too  deficient  in  available  water  to 
produce  a  good  crop  of  corn.  On  the  other  hand, 
heavy  clay  soils  are  slow  in  warming  up  and  thus  are 
not  suited  to  corn  culture.  The  western  prairie  soils, 
which  produce  most  of  the  corn  raised  in  the  United 
States,  are  composed  largely  of  silt. 

The  best  types  of  corn  soils  have  the  necessary 
mechanical  composition  for  the  production  of  good  crops 
of  sorghum,  cotton,  flax,  and  sugar  beets.  However, 
the  amount  of  available  plant  food  required  for  each  of 
these  crops  is  not  the  same. 

15.  Medium  Grass  and  Grain  Soils.  —  For  the  produc- 
tion of  grass  and  grain  a  larger  amount  of  water  is 
required  than  for  corn.  The  yield  is  determined  largely 
by  the  amount  of  water  which  the  soil  contains.  For 
an  average  rainfall  of  30  inches,  a  good  grass  and  grain 
soil  should  contain  about  1 5  per  cent  of  clay  and  60  per 
cent  of  silt.  Such  a  soil  ordinarily  holds  from  18  to  25 
per  cent  of  water.  Many  grass  and  grain  soils  have  less 
silt  and  more  clay.  A  soil  composed  of  about  30  per 
cent  each  of  fine  sand,  silt,  and  clay,  is  also  suitable 


PHYSICAL    PROPERTIES    OF    SOILS  25 

mechanically,  for  general  grain  production.  There  are 
a  number  of  different  types  of  grass  and  grain  soils, 
with  different  proportional  amounts  of  sand,  silt,  and 


Clay 


Very 

Fina 
Sand 

FIG.  ii.    Soil  Types. 

I.   Heavy  wheat  soil.      2.  Average  wheat  soil.      3.   Medium  wheat  and  grain 
soil.    4.   Corn  soil. 

clay.     Silt  soils,  however,  form  the  largest  part  of  the 
grain  soils  of  the  United  States. 

16.  Wheat  Soils.  —  For  wheat  production,  soils  of 
closer  texture  are  required  than  for  pther  small  grains. 
There  are  three  classes  of  wheat  soils.  In  the  first 


26  SOILS    AND     FERTILIZERS 

(i  in  Fig.  n)  there  are  from  30  to  50  per  cent  of  clay 
particles,  mostly  disintegrated  limestone.  The  soil  of 
the  Red  River  Valley  of  the  North  belongs  to  this  class. 
The  surface  soil  contains  from  7  to  10  per  cent  of 
vegetable  matter  and  the  subsoil  about  25  per  cent  of 
limestone  in  a  very  fine  state  of  division.  For  the  pro- 
duction of  wheat,  the  subsoil  should  have  a  good  store 
of  water. 

The  second  type  of  wheat  soil  (2  in  Fig.  n)  has  less 
clay  and  more  silt.  Many  prairie  subsoils  which  pro- 
duce good  crops  of  wheat  contain  about  25  per  cent  of 
sand,  50  per  cent  of  silt,  and  from  18  to  25  per  cent  of 
clay.  Soils  of  this  class  when  well  stocked  with  moisture 
in  the  spring  produce  good  crops  of  wheat,  but  are  not 
able  to  withstand  drought  so  well  as  soils  of  the  first 
class ;  during  wet  seasons,  however,  the  yields  are  larger 
than  on  heavier  clay  soils. 

To  the  third  class  of  wheat  soils  (3  in  Fig.  n)  belong 
those  which  are  composed  mainly  of  silt,  containing 
usually  75  per  cent,  and  from  10  to  15  per  cent  of 
clay.  The  high  per  cent  of  fine  silt  gives  the  soil  clay- 
like  properties.  Soils  of  this  class  are  adapted  to  a 
great  variety  of  crops.  For  the  production  of  wheat  it 
is  essential  that  a  good  supply  of  organic  matter  be 
maintained  in  such  soils  so  as  to  bind  together  the  soil 
particles.  The  special  peculiarities  of  the  different 
grain  crops  as  to  soil  requirements  are  discussed  in 
connection  with  the  food  of  crops. 


PHYSICAL     PROPERTIES     OF     SOILS 


MECHANICAL  COMPOSITION  OF  SOIL  TYPES  9 


KIND  OF  SOIL 

HEAVY 
WHEAT 

MEDIUM 
WHEAT 

AND     . 

CORN 

POTATO, 

ETC. 

GRAIN 

Name  of  Particles 

Size  in  Millim. 

1 

2 

3 

4 

5 

Medium  sand 

0.5  to  0.25 



3-i8 

1.20 

24.60 

59.04 

Fine  and  very 

fine  sand 

0.25  to  0.05 

6.18 

21.43 

4.14 

21.51 

5.60 

Silt 

0.05  to  o.oi 

20.25 

27.75 

44-35 

11.08 

9.07 

Fine  silt 

o.oi  to  0.005 

10-35 

17.60 

30-75 

12.  8l 

19-33 

Clay 

O.OO5 

57.00 

25.00 

'5-45 

22.80 

4.05 

Total  volatile 

6.22 

5.04 

4.11 

7.20 

2.91 

1.  A  heavy  wheat  soil  from  the  Red  River  Valley,  —  the  clay 
consists  largely  of  disintegrated  limestone. 

2.  Medium  wheat  soil  from  Western  Minnesota. 

3.  A  loam  soil  adapted  to  grasses  and  grains.     From  Minnesota 
Experiment  Station. 

4.  A  corn  soil  from  Southwestern  Minnesota. 

5.  A  potato  soil  from  Eastern  Minnesota. 

17.  Sandy,  Clay,  and  Loam  Soils.  —  Ordinarily  in 
agricultural  literature,  the  term  'sandy,'  'clay,'  or  'loam' 
is  used  to  designate  the  prevailing  character  of  a 
soil.  Sandy  soils  usually  contain  90  per  cent  or  more 
of  silica  or  chemically  pure  sand.  The  term  '  light 
sandy  soil'  is  sometimes  used  to  indicate  that  the 
soil  is  easily  worked,  while  'heavy  clay'  means  that 
the  soil  offers  great  resistance  to  cultivation.  Many 
soils  which  are  clay-like  in  character  are  not  composed 


28 


SOILS     AND     FERTILIZERS 


very  largely  of  clay.  There  are  subsoils  in  the  western 
states  which  have  clay-like  characteristics  but  contain 
only  about  15  per  cent  of  clay,  the  larger  part  of  the 
soil  being  silt.  A  loam  soil  is  a  mixture  of  sand  and 
clay ;  if  clay  predominates,  it  is  a  clay  loam,  while  if 
sand  predominates,  it  is  a  sandy  loam. 


RELATION  OF  THE  SOIL  TO  WATER  AND  AIR 

18.  Amount  of  Water  required  by  Crops.  —  Experi- 
ments show  that  it  takes  from  275  to  375  pounds  of 
water  to  produce  a  pound  of  dry  matter  in  a  grain  crop. 
In  order  to  produce  an  acre  of  average  wheat,  350  tons 
of  water  are  needed.  The  amount  of  water  required 
for  the  production  of  an  acre  of  various  crops  is  as 
follows  :  ^ 


AVERAGE  AMOUNT 
TONS  WATER 

MINIMUM  AMOUNT 
TONS  WATER 

Clover     

AOO 

•JIO 

Potatoes      

4OO 

MB 

Wheat    

•3CO 

300 

Oats  
Peas        

375 

-ije 

300 

•3QO 

Corn                        . 

•3QO 

Grapes 

77C 

Sunflowers17      

J/3 
6000 



The  amount  of  water  required  for  the  production  of 
crops  in  humid  and  arid  regions  has  not  been  exten- 


PHYSICAL     PROPERTIES    OF    SOILS  2Q 

sively  investigated.  Ordinarily  crop  yield  is  directly 
proportional  to  and  dependent  upon  the  water  supply. 
The  rainfall  during  the  time  of  growth  is  frequently 
less  than  the  amount  of  water  required  for  the  produc- 
tion of  the  crop.  One  inch  of  rainfall  is  equal  to  about 
112  tons  of  water  per  acre.  An  average  of  two  inches 
per  month  during  the  three  months  of  crop  growth  is 
equivalent  to  only  675  tons,  a  large  part  of  which  is  lost 
by  surface  drainage  and  by  evaporation.  Hence  it  is 
that  the  rainfall  during  an  average  growing  season  is 
less  than  the  amount  of  water  required  to  produce 
crops,  and  consequently  the  water  stored  up  in  the 
subsoil  must  be  drawn  upon  to  a  considerable  extent. 
Inasmuch  as  the  soil's  reserve  supply  of  water  is  such 
an  important  factor  in  crop  production,  it  follows  that 
the  capacity  of  the  subsoil  for  storing  up  and  supplying 
water  as  needed  is  a  matter  of  much  importance,  par- 
ticularly since  the  power  of  the  soil  for  absorbing  and 
retaining  water  may  be  influenced  by  cultivation  and 
manuring.  Before  discussing  the  influence  of  cultiva- 
tion upon  the  soil  water,  the  forms  in  which  water  is 
in  the  soil  should  be  studied.  It  is  present  in  three 
forms:  (i)  bottom  water,  (2)  capillary  water,  and  (3) 
hydroscopic  water. 

19.  Bottom  Water  is  that  which  stands  in  the  soil  at 
a  general  level,  and  fills  all  the  spaces  between  the  soil 
particles.  Its  distance  from  the  surface  can  be  told  in 
a  general  way  by  the  depth  of  surface  wells.  Bottom 


3O  SOILS    AND     FERTILIZERS 

water  is  of  service  to  growing  crops  when  it  is  at  such 
a  depth  that  it  can  be  brought  to  the  plant  roots  by 
capillarity,  but  when  too  near  the  surface,  so  that  the 
roots  are  immersed,  the  conditions  are  unfavorable  for 
crop  growth.  When  the  bottom  water  can  be  brought 
within  reach  of  the  roots  by  capillarity,  a  crop  has  an 
almost  inexhaustible  supply.  In  many  soils  known  as 
old  lake  bottoms,  such  a  condition  exists. 

20.    Capillary  Water.  —  The  water  held  in  the  minute 
spaces  above  the  bottom  water  is  known  as  the  capillary 

water.  The  capillary  spaces 
of  the  soil  are  the  small  spaces 
between  the  soil  particles  in 
which  water  is  held  by  surface 
tension,  the  force  acting  be- 
tween the  soil  and  the  water 
FIG.  12.  Water  Film  surrounding  being  greater  than  the  force 

Soil  Particles.  of  gravity.       If  a  series  Qf  glass 

tubes  of  different  diameters  be  placed  in  water,  it  will  be 
observed  that  in  the  smaller  tubes  water  rises  much 
higher  than  in  the  larger.  The  water  rises  in  all  of 
the  tubes  until  a  point  is  reached  where  the  force  of 
gravity  is  equal  to  the  force  of  surface  tension.  In 
the  smaller  tubes  surface  tension  is  greater  than  the 
force  of  gravity,  and  the  water  is  drawn  up  into  the 
tube  inversely  proportional  to  its  diameter.  In  the 
larger  tubes  the  surface  tension  is  less  and  the  water 
is  raised  only  a  short  distance.  There  are  present  in  the 


PHYSICAL    PROPERTIES    OF    SOILS 


soil  many  spaces  which  are  capable  of  taking  up  water 

in  the  same  way.     The  height  to  which  water  can  be 

raised    by   capillarity   de-- 

pends  upon  the    size  and 

arrangement   of    the    soil 

particles,  it  may  be  to    a 

height    of    several     feet. 

Ordinarily,    however,    the 

capillary   action  of  water 

is  confined  to  a  few  feet. 

The  arrangement   of   the 

soil     particles    influences 

greatly  the  capillary  power 

of  a  soil.      Usually  from 

30  to  60  per  cent  of  the 

bulk  of  a  soil  is  air  space ; 

by    compacting,    the    air 

spaces  are  decreased ;  by 

stirring,  they  are  increased. 

In  soils  of  close   texture, 

as  heavy  clays,  an  increase 

in  air  spaces  results   in  an    FIG.  13.   Showing  Rise  of  Water  in 

increase  of  capillary  Spaces  Capillary  and  other  Tubes. 

and  of  water-holding  capacity,  while  in  other  soils,  as 
coarse  sandy  soils,  increasing  the  air  spaces  decreases 
the  capillary  spaces  and  the  water-holding  capacity. 
The  best  conditions  for  crop  production  exist  when  the 
soil  contains  water  to  the  extent  of  about  40  per  cent 
of  its  total  capacity  for  saturation. 


32  SOILS  AND   FERTILIZERS 

21.  Hydroscopic  Water.  —  By   hydroscopic   water  is 
meant  the  water  that  is  held  mechanically  in  the  soil 
and   is  not    removed   by  air   drying.      The  air  which 
occupies  the  non-capillary  spaces  of  the  soil  is  charged 
with  moisture  in  proportion  to  the  water  in  the  soil. 
Under  normal  conditions  the  soil  atmosphere  is  nearly 
saturated.     When  soils  have  exhausted  their  capillary 
water,  the  water  in  the  soil  atmosphere  is  correspond- 
ingly reduced.      The  available   supply  in  other   forms 
being   exhausted,   the   hydroscopic   water   cannot   con- 
tribute to  pjant  growth  unless  supplemented  by  heavy 
fogs. 

22.  Loss   of   Water    by    Percolation.  —  Whenever  a 
soil    becomes    saturated,    percolation   or    a    downward 
movement  of  the  water  begins.     The  extent  to  which 
losses   by    percolation   may  occur   depends    upon    the 
character   of    the    soil    and    the    amount   of    rainfall. 
When   soils   are   covered   with   vegetation,    the    losses 
are  less  than  from  barren  fields.     In  all  soils  which 
have  only  a  limited  number  of  capillary  spaces  and  a 
large  number  of  non-capillary  spaces,  the  amount  of 
water  which  can  be  held  above  the  bottom  water  is 
small.     From  such  soils  the  losses  by  percolation  are 
greater  than   from  soils  which   have  a   larger  number 
of  capillary  spaces,  and  a  smaller  number  of  non-capil- 
lary spaces.     In  coarse  sandy  soils  many  of  the  spaces 
are  too  large  to  be  capillary. 

If  all  of  the  water  which  falls  on  some  soils  could 


PHYSICAL    PROPERTIES   OF   SOILS  33 

be  retained  and  not  carried  beyond  the  reach  of  crops 
by  percolation,  there  would  be  an  ample  supply  for 
agricultural  purposes.  The  texture  of  the  soil  may  be 
changed  by  cultivation  and  by  the  use  of  manures  so 
as  to  prevent  losses  by  percolation.  If  the  soil  is  of 
very  fine  texture,  as  a  heavy  clay,  percolation  is  slow, 
and  before  the  water  has  time  to  sink  into  the  soil, 
evaporation  takes  place.  With  good  cultivation,  the 
water  is  able  to  penetrate  to  a  depth  beyond  the  im- 
mediate influence  of  evaporation.  Compacting  an  open 
porous  soil  by  rolling,  checks  rapid  percolation  and  pre- 
vents the  water  from  being  carried  beyond  the  reach  of 
plant  roots.  Thus  it  will  be  seen  that  the  treatment 
necessary  to  prevent  excessive  losses  by  percolation, 
varies  with  different  soils.  In  regions  of  heavy  rain- 
fall and  mild  winters  the  losses  of  both  water  and  plant 
food  by  percolation  are  often  large. 

23.  Loss  of  Water  by  Evaporation.  —  The  factors 
which  influence  evaporation  are  temperature,  humidity, 
and  rate  of  movement  of  the  air.  When  the  air  con- 
tains but  little  moisture  and  is  heated  and  moving 
rapidly,  the  most  favorable  conditions  for  evaporation 
exist.  In  semi-arid  regions  the  losses  of  water  by 
evaporation  are  much  greater  than  by  percolation. 
The  dry  air  comes  in  contact  with  the  soil,  the  soil 
atmosphere  gives  up  its  water  taken  from  the  soil, 
and,  unless  checked  by  cultivation,  the  subsoil  water  is 
brought  to  the  surface  by  capillarity  and  lost.  In  porous 


34  SOILS   AND   FERTILIZERS 

soils  a  greater  freedom  of  movement  of  the  air  is  possi- 
ble, which  increases  the  rate  of  evaporation.  When  the 
surface  of  the  soil  is  covered  with  a  layer  of  finely  pul- 
verized earth,  or  with  a  mulch,  excessive  losses  by 
evaporation  cannot  take  place,  because  a  material  of 
different  texture  is  interposed  between  the  soil  and  the 
air. 

24.  Loss    of    Water    by  Transpiration.  —  Losses   of 
water   may  also   occur  from  the    leaves  of    plants   by 
the    process   known   as    transpiration.      Helriegel   ob- 
served that  during  some  years  100  pounds  more  water 
were  required  to  produce  a  pound  of  dry  matter  than  in 
other  years,  because  of  the  difference  in  the  amount  of 
water  lost  in  this  way.     The  loss  of  water  by  evapora- 
tion can  be  controlled  by  cultivation,  but  the  loss  by 
transpiration  can   be  only  indirectly  influenced.     Hot, 
dry  winds  may  cause  crops  to  wilt  because  the  water 
lost  by  transpiration   exceeds   the  amount  which   the 
plant  takes  from  the  soil. 

25.  Drainage.  —  Good  drainage  is  essential  in  order 
to  properly  regulate  the  water  supply.     An  excess  of 
water  in   the  soil   is  equally  as   injurious  as  a  scant 
amount.     If  the  water  which  falls  on  the  land  is  allowed 
to  flow  over  the  surface  and  is  not  retained  in  the  soil, 
there  is  not  sufficient  reserve  water  for  crop  growth. 
The  object  of  good  drainage  is  to  store  as  much  water 
as  possible  in  the  subsoil  and  prevent  surface  accumu- 


PHYSICAL   PROPERTIES   OF   SOILS  35 

lation  and  loss.  Good  drainage  is  accomplished  by 
thorough  cultivation,  and  in  regions  of  heavy  rainfall, 
by  tile  drainage.  Well-drained  land  is  warmer  in  the 
spring,  has  a  larger  reserve  store  of  water,  and  is  in 
better  condition  for  crop  growth.  Many  swampy  lands 
are  highly  productive  when  properly  drained.  A  high 
state  of  productiveness  cannot  be  maintained  without 
suitable  provision  for  drainage.  When  the  pores  of  the 
soil  are  rilled  with  water,  air  is  excluded  and  the  neces- 
sary chemical  and  bacteriological  changes  which  result 
in  rendering  plant  food  available  fail  to  take  place.  The 
drainage  of  wet  and  low  lands  forms  an  important  fea- 
ture of  rural  engineering. 

26.  Influence  of  Forest  Regions.  —  The  deforesting  of 
large  areas  near  the  sources  of  rivers  has  an  injurious 
influence  upon  the  moisture  content  of  adjoining  farm 
lands.  By  cutting  over  and  leaving  barren  large  tracts, 
less  water  is  retained  in  the  soil.  Also  near  forests  the 
air  has  a  higher  moisture  content,  due  to  the  water  given 
off  by  evaporation.  Lands  adjacent  to  deforested  dis- 
tricts lose  water  more  rapidly  by  evaporation,  because 
the  air  is  so  much  drier.  In  Section  24  it  is  stated  that 
losses  of  water  by  transpiration  can  be  indirectly  influ- 
enced. This  can  be  accomplished  by  retaining  the 
forests. 

Good  drainage  is  necessary  not  only  for  individual 
farms,  but  also  for  an  entire  community.  Good  storage 
capacity  in  the  form  of  forest  lands,  for  the  surplus 


36  SOILS   AND    FERTILIZERS 

water  which  accumulates  near  the  sources  of  large 
rivers  is  also  a  necessity  to  agriculture. 

The  three  ways  by  which  crops  are  deprived  of  water 
are,  — (i)  percolation,  (2)  evaporation,  and  (3)  transpira- 
tion. With  proper  methods  of  cultivation  losses  by  per- 
colation and  evaporation  may  be  controlled,  and  losses 
by  transpiration  may  be  reduced. 

INFLUENCE  OF  CULTIVATION  UPON  THE  WATER 
SUPPLY  OF  CROPS 

27.  Capillarity  influenced  by  Cultivation.  —  The  capil- 
larity and  moisture  content  of  soils  can  be  influenced  by 

different  methods  of 
cultivation,  as  rolling 
and  subsoiling,  deep 
plowing,  and  shallow 
surface  cultivation. 
The  treatment  which 
a  soil  should  receive 

in  order  to  insure  the  best  water  supply  for  crops  must 
vary  with  the  rainfall,  the  nature  of  the  soil,  and  the 
crop  to  be  produced.  It  frequently  happens  that  the 
annual  rainfall  is  sufficient  to  produce  good  crops,  but  it 
is  too  unevenly  distributed,  and  hence  is  not  all  utilized 
to  the  best  advantage.  Losses  of  water  occur  through 
surface  drainage,  percolation,  and  excessive  evaporation, 
but  if  it  were  properly  stored  in  the  subsoil  and  conserved 
by  cultivation,  these  losses  would  be  prevented  and  there 
would  be  sufficient  for  crop  production. 


PHYSICAL    PROPERTIES    OF    SOILS  3/ 

It  is  possible,  to  a  great  extent,  to  vary  the  cultiva- 
tion so  as  to  conserve  the  moisture  of  the  soil  to  meet 
the  requirements  of  crops. 

28.  Shallow  Surface  Cultivation.  —  When  shallow  sur- 
face cultivation  is  practiced,  the  capillary  spaces  near 
the  surface  are  destroyed  and  the  direct  connection  of 
the  subsoil  water  with 
the  upper  layer  is 
broken,  the  ground  is 
covered  with  finely 
pulverized  earth,  and 
the  soil  particles  have  FlG-  l6-  Soil  without  Surface  Cultivation- 
been  disturbed  so  there  is  not  that  close  contact  which 
enables  the  water  to  pass  from  particle  to  particle.  When 
evaporation  takes  place  there  is  a  movement  of  the  sub- 
soil water  to  the  surface,  but  if  that  is  covered  with  a 
layer  of  fine  earth,  the  subsoil  water  cannot  readily  pass 
through  such  a  medium,  and  evaporation  is  checked. 
Hence  shallow  surface  cultivation  conserves  the  soil 
moisture. 

The  means  by  which  surface  cultivation  is  accom- 
plished must,  of  necessity,  vary  with  the  nature  of  the 
soil.  If  a  harrow  is  used,  the  pulverization  should  be 
complete,  if  a  disk,  the  teeth  should  be  set  at  an  angle, 
and  not  perpendicularly,  so  as  to  prevent,  as  suggested 
by  King,13  the  formation  of  hard  ridges  which  hasten 
evaporation.  When  the  disk  is  set  at  an  angle,  a  layer 
of  soil  is  completely  cut  off,  and  the  capillary  connec- 


SOILS    AND    FERTILIZERS 


tion  with  the  subsoil  is  broken.  Surface  cultivation 
should  be  from  two  to  three  inches  deep,  and  the  finer 
the  condition  in  which  the  surface  soil  is  left,  the  better. 
Shallow  surface  cultivation  does  not  mean  that  the  soil 
should  not  be  previously  well  prepared  by  thorough  cul- 
tivation. It  can  be  practiced  in  connection  with  deep 
plowing,  shallow  plowing,  subsoiling,  or  rolling ;  in  fact, 
it  can  be  combined  with  any  method  of  treating  the 
land,  and  is  an  effectual  means  of  conserving  soil  mois- 
ture. The  following  example  shows  the  extent  to  which 
shallow  surface  cultivation  may  conserve  the  soil  water : 14 


1 

PER  CENT  OF  WATER  IN  CORNFIELD 

With  shallow  surface 
cultivation 

Without  shallow  surface 
cultivation 

Soil,  depth  3  to  9  inches 
Soil,  depth  9  to  15  inches 

14.12 
17.21 

8.02 
12.38 

29.  Cultivation  after  a  Rain. — When  evaporation 
takes  place  immediately  after  a  rain,  not  only  is  there 
a  loss  of  the  water  which  has  fallen,  but  there  may 
also  be  a  loss  of  the  subsoil  water  by  translocation,  if 
nothing  be  done  to  prevent.13  After  a  rain,  soils  should 
be  cultivated  as  soon  as  the  implements  will  work  well, 
so  as  to  check  evaporation  and  prevent  the  formation 
of  a  crust.  The  following  example  shows  the  extent 
to  which  the  subsoil  water  may  be  brought  to  the 
surface : u 


PHYSICAL    PROPERTIES    OF    SOILS 


39 


. 

PER  CENT  OF  WATER 

Surface  soil, 
i  to  3  inches 

Subsoil, 
6  to  12  inches 

Before  the  shower  

9-77 

22.11 

18.22 
16.70 

After  the  shower     

The  rainfall  was  sufficient  to  have  raised  the  water 
content  of  the  surface  soil  to  20.77  Per  cent.  The  sub- 
soil showed  a  loss  of  1.52  per  cent,  while  the  surface 
soil  showed  a  gain  of  1.34  per  cent  in  addition  to  the-, 
water  received  from  the  shower.  If  evaporation  begins 
before  the  equilibrium  is  reestablished,  there  is  lost,  not 
only  the  water  from  the  shower,  but  also  the  water 
which  has  been  translocated  from  the  subsoil  to  the 
surface.  Hence  the  importance  of  shallow  surface 
cultivation  immediately  after  a  rain. 

When  the  subsoil  contains  a  liberal  supply  of  water, 
and  the  surface  soil  a  minimum  amount,  there  is  after  a 
shower  a  movement  of  the  subsoil  water  to  the  surface. 
The  soil  particles  at  the  surface  are  surrounded  with 
films  of  water  which  thicken  at  the  expense  of  the  sub- 
soil water.  Surface  tension  is  the  cause  of  this  movement 
of  the  water  to  the  surface,  and  under  the  conditions 
stated  it  is  temporarily  greater  than  the  force  of  gravity. 

A  hard,  thin  crust  should  never  be  allowed  to  form 
after  a  rain,  because  it  hastens  losses  by  evaporation, 
while  a  soil  mulch  formed  by  surface  cultivation  has  the 
opposite  effect 


4<D  SOILS    AND    FERTILIZERS 

30.  Rolling.  —  The  use  of  heavy  rollers  for  compact- 
ing the  soil  is  beneficial  in  a  dry  season  on  a  soil  con- 
taining  large   proportions   of   sand   and    silt.     Rolling 
compacts  the  land  and  improves  the  capillary  condi- 
tion, enabling  more  of  the  subsoil  water  to  be  brought 
to  the  surface.     Experiments  show  that  when  land  is 
rolled  the  amount  of  water  in  the  surface  soil  is  in- 
creased.    This  increase  is,  however,  at  the  expense  of 
the  subsoil  water.16     Unless  rolled  land  receives  surface 
cultivation,  excessive  losses  by  evaporation,  due  to  im- 
proved capillarity,  may  result.     The  use  of  the  roller  on 
heavy  clay  during   a  wet   season   results   unfavorably. 
Occasionally,  light  rolling  of  clay  land  is  beneficial  in 
pulverizing  the  clods. 

In  some  localities  rolling  and  subsequent  surface  cul- 
tivation are  not  admissible  on  account  of  drifting  of  the 
soil,  caused  by  heavy  winds. 

31.  Subsoiling.  —  By  subsoiling  is  meant  pulverizing 
the  soil  below  the  furrow  slice.     This  is  accomplished 
with   the   subsoil   plow,  which  simply  loosens  without 
bringing  the  subsoil  to  the  surface.     The  object  of  sub- 
soiling  is  to  enable  the  land  to  retain,  near  the  surface, 
more  of  the  rainfall.     Heavy  clay  lands  are  sometimes 
improved  by  occasional   subsoiling,  but   its   continued 
practice   is   not  desirable.     For  orcharding   and   fruit 
growing,  it  is  frequently  resorted  to,  but  is  not  bene- 
ficial on  soils  containing  large  amounts  of  sand  and  silt. 
Rolling  and  subsoiling  are  directly  opposite  in  effect. 


PHYSICAL    PROPERTIES    OF    SOILS  41 

Soils  which  are  improved  by  rolling  are  not  improved 
by  subsoiling.  The  additional  expense  involved  should 
be  considered  when  subsoiling  is  to  be  resorted  to.  Ex- 
periments have  not  as  yet  been  sufficiently  decisive  to  indi- 
cate all  of  the  conditions  most  favorable  for  this  practice. 

32.  Fall  Plowing  followed  by  surface  cultivation  con- 
serves the  soil  water,  by  checking  evaporation  and  leav- 
ing the  land  in  better  condition  to  retain  moisture.     If 
conditions  allow,  fall  plowing  can  be  followed  by  surface 
cultivation,  but  in  some  localities  heavy  winds  prevent 
this.     It  is  generally  better  to  give  the  surface  cultiva- 
tion early  the  following  spring.     Clay  land  should  be 
left  in  a  ridged  condition  when  fall  plowed,  so  as  to  ex- 
pose a  greater  surface  area  and  to  allow  a  better  oppor- 
tunity for  the  water  to  sink  into  the  subsoil.     Evaporation 
may  take  place  from  unplowed  land  during  the  fall,  and 
in  the  spring  the  soil  contain  appreciably  less  water  than 
plowed  land.     By  fall  plowing  it  is  possible  to  carry  over 
a  water  balance  of  100  tons  or  more  from  one  year  to 
the  next. 

33.  Spring  Plowing.  —  When  land  is  plowed  late  in 
the  spring  there  has  been  a  loss  of  water  by  evapora- 
tion, and  the  soil  has  not  been  able  to  store  up  as  much 
of  the  rain  and  snow  as  if  fall  plowing  had  been  prac- 
ticed.15    Then,  too,  dry  soil  is  plowed  under  and  moist 
soil  brought  to  the  surface,  and  if  surface  cultivation  does 
not  follow,  this  moisture  is  readily  lost  by  evaporation, 


42 


SOILS   AND    FERTILIZERS 


good  capillary  connection  of  the  surface  soil  and  subsoil 
is  not  obtained,  and  the  furrow  slice  soon  becomes  dry. 


PER  CENT  OF  WATER  in14 

Fall-plowed 
land 

Spring-plowed 
land 

24.7 
26.6 
28.8 

22-4 
24.1 
26.5 

2.37  per  cent 

Surface  cultivation  should  immediately  follow  spring 
plowing. 

34.  Mulching.  —  The  use  of  well-rotted  manure  or 
straw,  spread  over  the  surface  as  a  mulch,  prevents 
evaporation.  In  forests  the  leaves  form  a  mulch  which 
is  an  important  factor  in  maintaining  the  water  supply. 
In  order  that  a  mulch  be  effectual,  it  must  be  com- 
pacted, —  a  loose  pile  of  straw  is  not  a  mulch.  In 
reclaiming  lands  gullied  by  water,  mulching  is  very 
beneficial,  also  a  light  mulch  may  be  used  to  encourage  the 
growth  of  grass  on  a  refractory  hillside.  Surface  cultiva- 
tion and  mulching  may  be  advantageously  combined.14 


Mulched  straw- 
berry patch 

Unmulched 

Soil    2  to    5  inches      

18.12 

II  .17 

Soil    6  to  12  inches      

22.18 

I8.I4 

Soil  12  to  1  8  inches      

24..  31 

21.  II 

PER  CENT  OF  WATER  IN 


PHYSICAL    PROPERTIES   OF    SOILS  43 

35.  Depth  of  Plowing.  —  The  depth  to  which  a  soil 
should  be  plowed  in  order  to  give  the  best  results  must, 
of  necessity,  vary  with  the  conditions.  Deep  plowing 
of  sandy  land  is  not  advisable,  particularly  in  the  spring. 
On  clay  land  deeper  plowing  should  be  the  rule.  The 
longer  a  soil  is  cultivated,  the  deeper  and  more  thorough 
should  be  the  cultivation.  While  shallow  plowing  is 
admissible  on  new  prairie  land,  deeper  cultivation 
should  be  practiced  when  the  land  has  been  cropped 
for  a  series  of  years.  Also,  the  depth  of  plowing  should 
be  regulated  by  the  season.  In  prairie  regions,  and  in 
the  northwestern  part  of  the  United  States,  shallow 
plowing  is  more  generally  practiced  than  in  the  eastern 
states.  Deep  plowing  in  the  fall  gives  better  results 
than  in  the  spring.  It  is  not  a  wise  plan  to  plow  to  the 
same  depth  every  year.  Professor  Roberts  says : 16  "  If 
plowing  is  continued  at  one  depth  for  several  seasons, 
the  pressure  of  the  implement  and  the  trampling  of  the 
horses  in  time  solidify  the  bottom  of  the  furrow,  but  if 
the  plowing  is  shallow  in  the  spring  and  deep  in  sum- 
mer and  fall,  the  objectionable  hardpan  will  be  largely 
prevented." 

In  regions  of  scant  rainfall  deep  plowing  of  silt 
soils  should  be  done  only  at  intervals  of  three  or 
five  years,  but  with  an  average  rainfall,  deep  plowing 
should  be  the  rule  on  soils  of  close  texture.  The 
depth  of  plowing  should  be  varied  to  meet  the  re- 
quirements of  the  crop  and  soil  and  the  amount  of 
rainfall. 


44 


SOILS   AND    FERTILIZERS 


36.  Permeability  of  Soils.  — The  rapidity  with  which 
water  sinks  into  the  soil  after  a  rain  depends  upon 
the  nature  of  the  soil,  and  the  cultivation  which  it  has 
received.  Shallow  surface  cultivation  leaves  the  soil  in 
good  condition  to  absorb  water.  When  the  surface  is  hard 
and  dry  a  large  per  cent  of  the  water  which  falls  on  roll- 
ing land  is  lost  by  surface  drainage.  Soils  of  close  tex- 
ture, which  contain  but  few  non-capillary  spaces,  offer  the 
greatest  resistance  to  the  downward  movement  of  water. 
A  soil  is  permeable  when  it  is  of  such  a  texture  that 

it  does  not  allow  the 
water  to  accumulate 
and  clog  the  non-capil- 
lary spaces.  Cultiva- 
tion may  change  the 
tilth  of  even  a  clay  soil 
to  such  an  extent  as  to 
render  it  permeable. 
Deep  plowing  increases 
permeability.  In  regions  of  heavy  rains,  increased 
permeability  is  very  desirable  for  good  crop  production 
on  heavy  clays.  Sandy  and  loamy  soils  have  naturally 
a  high  degree  of  permeability,  and  it  is  not  necessary 
that  it  should  be  increased. 


FIG.  17.     Sandy  Soil  without  Manure. 


37.  Fertilizers.  • —  When  water  contains  dissolved 
salts,  it  is  more  susceptible  to  the  influence  of  surface 
tension,  and  is  more  readily  brought  to  the  surface  of  the 
soil.  In  commercial  fertilizers  soluble  salts  are  present. 


PHYSICAL    PROPERTIES    OF    SOILS 


45 


However,  the  beneficial  effect  of  these  upon  the  moisture 
content  of  soils  is  liable  to  be  overestimated,  because 
the  fertilizer  undergoes  fixation  when  applied,  and  does 
not  remain  in  a  soluble  condition.  Fertilizers  containing 
soluble  salts  exercise  a  favorable  influence  upon  the 
moisture  content  of  soils,  but  the  extent  of  this  influence 
has  never  been  determined  under  field  conditions. 

38.  Farm  Manures.  —  Farm  manures  exercise  a  bene- 
ficial effect  upon  the  moisture  content  of  soils.  When 
the  manure  is  worked  into  a  soil,  the  coarse  soil  particles 
and  masses  bind 
together,  and  the 
non-capillary 
spaces  are  made 
capillary.  Free 
circulation  of  the 
air,  which  in- 
creases evapora- 

^    .     ,  FIG.  18.  Sandy  Soil  with  Manure. 

tion,  is  prevented 

when  a  sandy  soil  is  manured.  When  soils  are  manured 
they  retain  more  water,  as  shown  by  the  following 
example : 14 


95  PER  CENT  FINE 

FINE  SANDY 

SANDY  SOIL 

SOIL. 

AND  5  PER 

PER  CENT 

CENT  MANURE. 

PER  CENT 

Capacity  for  holding  water    .... 

25 

42 

46  SOILS    AND    FERTILIZERS 

The  manure  enables  the  soil  to  retain  more  of  the 
moisture  near  the  surface  and  prevents  losses  by  perco- 
lation. The  difference  in  moisture  content  between 
manured  and  unmanured  land  is  particularly  noticeable 
in  a  dry  season.14 


SANDY  SOIL 
WELL  MANURED. 
WATER 

SANDY  SOIL 
UNMANURED. 
WATER 

Soil  I  to  6  inches      

Per  Cent 
IO.CO 

Per  Cent 
8.10 

Coarse  leached  manure  may  have  just  the  opposite 
effect  by  producing  an  open  and  porous  condition  of  the 
soil. 

RELATION  OF  SOIL  TO  HEAT 

39.  Soil   Temperature.  —  The   way   in   which   a  soil 
responds  to  heat  and  cold  is  an  important  factor  in  its 
crop-producing  value.      A  soil   temperature  of  42°  to 
56°  F.  is  required  for  crop  growth,  and  the  best  condi- 
tions do  not  exist  until  the  soil  has  reached  a  tempera- 
ture of  60°  to  70°  F.     During  cold  springs  in  northern 
latitudes  the  soil  is  often  so  cold  as  to  retard  the  germi- 
nation process,  and  to  affect  the  vitality  of  seeds,  caus- 
ing a  poor  stand  of  grain. 

40.  Heat  required  for  Evaporation.  —  It  is  estimated 
that  the  heat  required  to  evaporate  a  pound  of  water  at 
60°  F.  would  raise  the  temperature  of  1000  pounds  of 
water    i°  F.     When     water    evaporates,    the     soil    is 


PHYSICAL   PROPERTIES   OF   SOILS  47 

cooled,  and  if  the  heat  for  evaporation  is  all  furnished 
by  the  surrounding  soil,  it  materially  lowers  the  soil's 
temperature  and  unfavorably  affects  crop  growth.  In 
the  early  spring,  drying  winds  may  temporarily  lower 
the  soil  temperature  by  hastening  evaporation.  Much 
heat  is  unnecessarily  lost  in  evaporating  excessive 
amounts  of  water  which  should  be  removed  by  good 
systems  of  drainage. 

41.  Temperature  of  Drained  and  Undrained  Land. — 
The   surface   of   well-drained    land   is   usually   several 
degrees  warmer  than  that  of  poorly  drained  land.    Water 
being  a  poor  conductor  of   heat,  it   follows   that   soils 
which  are  saturated  are  slow  to  warm  up  in  the  spring. 
At  a  depth  of  2  or  3  feet  the  difference  in  tempera- 
ture between  wet  and  dry  soils  is  not  marked.     It  is  to 
be  observed  that  with  proper  systems  of  drainage  the 
surplus  water  is   removed  from    the    surface    soil   and 
stored  up  in  the  subsoil  for  future  use  by  the  crop,  and 
at  the  same  time  the  temperature  of  the  surface  soil  is 
raised,  thus  improving  the  conditions  for  growth.     The 
relation   of   drainage  to   the   temperature    and   proper 
supply  of  water  for  crop  growth,  receives  too  little  con- 
sideration in   field   practice.      When   the   land   is  well 
drained,  and  receives  early   cultivation,  the  conditions 
are  best. 

42.  Color  of  Soils  and  Absorption  of  Heat.  —  All  dark- 
colored   soils   have   greater   power  of   absorbing   heat 


48  SOILS   AND    FERTILIZERS 

than  those  light  in  color.  Schtibler  observed  a  differ- 
ence in  temperature  of  8°  C.  between  the  same  soils, 
when  given  a  white  coating  with  magnesia  and  a  black 
coating  with  lampblack.17  Black  humus  soils  usually 
contain  so  much  water  that  the  additional  heat  is  utilized 
for  evaporation,  and  this  results  in  the  soil  being  cooler 
than  light-colored  sandy  soil. 

43.  Specific  Heat  of  Soils.  —  Soils  have  a  low  specific 
heat ;  it  requires  only  about  one  fifth  as  much  to  raise  a 
pound  of  soil  i°  as  is  required  to  raise  a  pound  of  water 
i°.     When    soils  are  wet,  the  specific  heat  is  greatly 
increased,  and  they  respond  more  slowly  to  the  influ- 
ence of  the  sun's  rays.     Sand  has  the  lowest  specific 
heat  of  any  soil  constituent  and  retains  the  least  water, 
hence  sandy  soils  warm  up  more  readily  than  other  soils. 
On  the  other  hand,  clay  soils,  although  slower  to  warm 
up  in  the  spring,  retain  their  heat  longer. 

44.  Farm  Manures  and  Soil  Temperature.  —  When  the 
animal  and  vegetable  matter  of  the  soil  decays,  heat  is 
produced.     The  slow  oxidation  of  manure  in  the  soil 
yields  in  the  end  as  much  heat  as  if  the  dry  manure 
were  burned.     Whenever  combustion  or  oxidation  takes 
place,  heat  results. 

Manured  land  is  usually  i°  or  2°  warmer  in  the  spring 
than  unmanured  land.  It  has  been  estimated  that  the 
amount  of  organic  matter  which  undergoes  oxidation  in 
an  acre  of  rich  prairie  soil  produces  as  much  heat 


PHYSICAL    PROPERTIES    OF    SOILS  49 

annually  as  the  burning  of  a  ton  of  coal.9  The  addi- 
tional heat  in  well-drained  and  well-manured  land  is  an 
important  factor  in  stimulating  crop  growth,  particu- 
larly in  a  cold  backward  spring.  The  production  of 
heat  from  manure  is  utilized  in  the  case  of  hotbeds 
where  manure  in  rotting  raises  the  temperature  of  the 
soil.  When  soils  are  well  manured,  heat  is  retained 
more  effectually  and  crops  on  such  land  often  escape 
early  frosts. 

45.  Influence  of  Exposure  upon  Soil  Temperature.  — 
Land  with  a  southern   slope   receives   the   sun's   rays 
longer  and  at  a  better  angle  for  absorbing  heat  than 
land  sloping  to  the  north.     In  valleys  and  low  places 
the  soil  at  night  cools  more  rapidly  than   on   higher 
ground,  and  hence  crops  in  valleys  may  be  injured  by 
late   spring  and   early  autumn  frosts,  while  those   on 
higher  and  warmer  land  escape. 

46.  Influence  of  Cultivation  upon  Soil  Temperature.  — 

Thorough  cultivation  resulting  in  the  production  of  a 
fine  pulverized  seed  bed  enables  the  soil  to  absorb  a 
larger  amount  of  heat  than  if  left  in  a  rough  lumpy  con- 
dition. Cultivated  land  is  more  porous  and  allows 
greater  freedom  of  movement  of  water  into  the  subsoil. 
Warm  spring  rains  have  a  marked  effect  upon  the 
temperature  of  cultivated  soils  by  filling  the  pores  with 
warm  water.  The  influence  of  temperature  upon  nitri- 
fication is  discussed  in  Chapter  IV. 


5O  SOILS   AND   FERTILIZERS 

47.  Relation  of  Heat  to  Crop  Growth.  —  All  plant  life 
is  directly  dependent  upon  solar  heat  as  the  source  of 
energy  for  the  production  of  plant  tissue.     The  heat  of 
the  sun  is  the  main  force  at  the   plant's   disposal  for 
decomposing  water  and  carbon  dioxide  and  for  produc- 
ing starch,  cellulose,  and  other  compounds.     The  growth 
of  crops  is  the  result  of  the  transformation  of  solar  heat 
into  chemical  energy  which  is  stored  up  in  the  plant. 
When  the  plant  is  used  for  fuel  or  for  food,  the  quantity 
of  heat  produced  by  complete  oxidation  is  equal  to  the 
amount  required  for  the  formation  of  the  plant's  tissue. 

48.  Color  of  Soils.  —  The  principal  materials  which 
impart  color  to  soils  are  organic  and  iron  compounds. 
A  union  of  the  decaying  organic  matter  (humus)  with 
the  minerals  of  the  soil  produces  compounds  brown  or 
black  in  color,  and  consequently  soils  containing  large 
amounts  of  humus  are  dark-colored.     When  moist,  soils 
are  darker  than  when  dry,  and  soils  hi  which  the  organic 
matter  has  been  kept  up  by  the  use  of  manures  are 
darker  than  unmanured  soils.18    When  rich,  black,  prai- 
rie soils  lose  their  organic  matter  through  injudicious 
methods  of  cultivation,  or  when  in  chemical  analysis  it 
is  extracted,  the  soils  become  light-colored. 

The  red  color  of  soils  is  imparted  by  ferric  oxide ;  the 
yellow,  by  smaller  amounts  of  the  same  material.  A 
greenish  tinge  is  supposed  to  be  due  to  the  presence 
of  ferrous  compounds,  such  soils  being  so  close  in  tex- 
ture as  to  prevent  the  oxidizing  action  of  the  air.  Color 


PHYSICAL    PROPERTIES   OF   SOILS  51 

may  serve,  to  a  slight  extent,  as  an  index  of  fertility. 
Black  and  yellow  soils  are,  as  a  rule,  the  most  produc- 
tive, although  occasionally  black  soils  are  unproductive 
because  of  the  presence  of  acid  compounds  injurious  to 
vegetation.  The  main  reason  why  black  soils  are  so 
generally  fertile  is  because  they  contain  a  high  per  cent 
of  humus  and  nitrogen. 

49.  Odor  and  Taste  of  Soils.  —  Soils  containing  liberal 
amounts  of  organic  matter  have  characteristic  odors  due 
to  the  presence  of   aromatic   bodies   produced  by  the 
decomposition  of  organic  matter.      In  cultivated   soils 
these  have  a  neutral  reaction.     The  amount  of  aromatic 
compounds  in  soils  is  very  small     Poorly  drained  peaty 
soils  give  off  volatile  acid  compounds  when  dried. 

The  taste  of  soils  varies  with  the  chemical  composi- 
tion. Peaty  soils  usually  have  a  slightly  sour  taste,  due 
to  the  presence  of  organic  acids.  Alkaline  soils  have 
variable  tastes  according  to  the  prevailing  alkaline  com- 
pound. The  taste  of  a  soil  frequently  reveals  a  fault, 
as  acidity  or  alkalinity. 

50.  Power  of  Soils  to  absorb  Gases. — All  soils  pos- 
sess, to  a  variable  extent,  the  power  of  absorbing  gases. 
When  decomposing  animal  or  vegetable  matter  is  mixed 
with  soil,  the  gaseous  products  given  off  are  absorbed. 
Absorption  is  the  result  of  both  chemical  and  physical 
action.     The  chemical  changes  which  occur,  as  the  fixa- 
tion of  ammonia,  are  considered  in  the  chapter  on  fixa- 


52  SOILS   AND    FERTILIZERS 

tion.  The  organic  matter  of  the  soil  is  the  principal 
agent  in  the  physical  absorption  of  gases  ;  peat  has  the 
power  of  absorbing  large  amounts.  This  action  is  sim- 
ilar to  that  of  a  charcoal  filter  in  removing  noxious 
gases  from  water. 

51.  Relation  of  Soils  to  Electricity.  —  There  is  always 
a  certain  amount  of  electricity  in  both  the  soil  and  the 
air.     The  part  which  it  takes  in  plant  growth  is  not 
well  understood.     The  action  of  a  strong  current  upon 
the  soil  undoubtedly  results  in  a  change  in  chemical 
composition,  but  in  order  to  change  the  composition  of 
the   soil   so   as   to   render  the  unavailable  plant   food 
available,  a  current  destructive  to  vegetation  would  be 
required.     When  plants  are  subjected  to  too  strong  a 
current  of  electricity,  they  wilt  and  have  all  of  the  after- 
effects of  frost.     A  feeble  current  has  either  an  indif- 
ferent or  a  slightly  beneficial  effect  upon  crop  growth, 
but  not  sufficient  to  warrant  its  use  in  general  crop 
production  on  account  of  cost,  and  it  is  undoubtedly 
physiological  rather  than  chemical  in  its  action  unless 
it  be  in  the  favorable  influence  exerted  upon  nitrifica- 
tion.   The  electrical  conductivity  of  soils  has  been  taken 
by  Whitney  as  the  basis  for  the  determination  of  mois- 
ture.19   It  is,  however,  dependent  largely  upon  the  nature 
and  amount  of  dissolved  salts. 

52.  Importance  of  the  Physical  Study  of  Soils.  —  A 
study  of  the  physical  properties  of  soils  gives  much  val- 


PHYSICAL    PROPERTIES    OF    SOILS  53 

uable  information  regarding  their  probable  agricultural 
value ;  but  while  the  physical  properties  should  always 
be  taken  into  consideration,  they  should  not  form  the 
sole  basis  for  judging  the  character  of  a  soil,  because 
two  soils  from  the  same  locality  frequently  have  the 
same  general  physical  composition,  although  entirely 
different  crop-producing  power,  due  to  differences  in 
chemical  composition  and  amounts  of  available  plant 
food.  It  is  not  possible  from  a  physical  analysis  alone 
to  determine  the  agricultural  value  of  a  soil. 

Attempts  have  been  made  to  overestimate  the  value 
of  the  physical  properties  of  soils  and  to  explain  nearly 
all  soil  phenomena  on  the  basis  of  soil  physics,  but 
important  as  are  the  physical  properties,  it  cannot  be 
said  they  are  of  more  importance  than  the  chemical  or 
bacteriological.  In  fact,  the  four  sciences,  chemistry, 
physics,  geology,  and  bacteriology,  are  all  closely  con- 
nected and  each  contributes  its  part  to  our  knowledge 
of  soils. 


CHAPTER  II 

GEOLOGICAL  FORMATION  AND  CLASSIFICATION  OF 
SOILS 

53.  Agricultural  Geology.  —  The  geological  study  of 
a  soil  concerns  itself  with  the  past  history  of  that  soil, 
the  materials  out  of  which  it  has  been  produced,  together 
with  the  agencies  which  have  taken  part  in  its  forma- 
tion and  distribution.     Geologically,  soils  are  classified 
according   to   the   period   in   the  earth's  history  when 
formed,  and  also  according  to  the  agencies  which  have 
distributed  them.     The  principles  of  soil  formation  and 
distribution  should  be  understood,  because  of  their  im- 
portant bearing   upon   fertility.     Agricultural   geology 
forms  a  separate  branch  of  agricultural  science ;  in  this 
work  only  a  few  topics  especially  relating  to  soils  are 
treated. 

54.  Formation  of  Soils.  —  Geologists   state   that  the 
surface  of  the  earth  was  at  one  time  solid  rock.     It  is 
held  that  soils    have  been   formed  from  rock  by  the 
joint  action  of  the  various  agents:  (i)  heat  and  cold, 
(2)  water,  (3)  gases,  (4)  micro-organisms  and  other  forms 
of  vegetable  and  animal  life,  and  (5)  wind.     One  of  the 
best  evidences  that  soil  is  derived  from  rock  is  that  there 

54 


GEOLOGICAL    STUDY    OF    SOILS  55 

are  frequently  found  pieces  which  are  rotten,  and,  when 
crushed,  closely  resemble  the  prevailing  soil  of  the 
field.  This  is  particularly  true  of  clay  soils  where  there 
are  fragments  of  disintegrated  feldspar  that  when 
crumbled  are  similar  to  the  soil  in  which  the  feldspar 
was  embedded.  The  process  of  soil  formation  is  ex- 
tremely slow  and  the  various  agents  have  been  at  work 
for  an  almost  unlimited  period. 

Weathering  is  the  joint  action  upon  rocks  of  the  vari- 
ous atmospheric  agencies.  Some  rocks  are  more  sus- 
ceptible to  it  than  others,  and  in  different  localities  even 
the  same  kind  of  rock  may  vary  in  the  rapidity  with 
which  it  responds  to  weathering. 

55.  Action  of  Heat  and  Cold.  —  The  cooling  of  the 
earth's  surface,  followed  by  a  contraction  in  volume, 
resulted  in  the  formation  of  fissures  which  exposed  a 
larger  area  to  the  action  of  other  agencies.  The  un- 
equal cooling  of  the  rocks  caused  a  partial  separation 
of  the  different  minerals  of  which  the  rocks  were  com- 
posed, resulting  in  the  formation  of  smaller  rock  parti- 
cles from  the  larger  rock  masses.  This  is  well  illustrated 
by  the  familiar  splitting  and  crumbling  of  stones  when 
heated.  Shaler  estimates  that  a  variation  of  1 50°  F. 
will  make  a  difference  of  I  inch  in  the  length  of  a 
granite  ledge  100  feet  long.  As  a  result  of  changes  in 
temperature  there  is  a  lessening  in  cohesion  of  the  rock 
particles.  The  action  of  frost  also  is  favorable  to  soil 
formation.  The  freezing  of  water  in  rock  crevices 


50  SOILS    AND    FERTILIZERS 

results  in  breaking  up  the  rock  masses,  forming  smaller 
bodies.  The  force  exerted'  by  water  when  it  freezes  is 
sufficient  to  rend  large  rocks. 

56.   Physical  Action  of  Water.  —  Water  acts  upon  soils 
both  chemically  and  physically.     It  is  the  most  impor- 


FlG.  19.     Boulder  split  by  Frost. 
(Minnesota  Geological  and  Natural  History  Survey.) 

tant  agent  that  takes  a  part  in  soil  formation.  The  sur- 
face of  rocks  has  been  worn  away  by  moving  water  and 
in  many  cases  deep  ravines  and  cafions  have  been 
formed.  This  is  called  erosion.  The  pulverized  rock, 
being  carried  along  by  the  water  and  deposited  under 
favorable  conditions,  forms  alluvial  soil.  This  physical 


GEOLOGICAL  STUDY  OF  SOILS  57 

action  of  water  is  illustrated  in  the  workings  of  large 
rivers  where  the  pulverized  rock  particles  are  deposited 
along  the  river  and  at  its  mouth.  Large  areas  of  the 
soil  in  valleys  and  river  bottoms  have  been  formed  in 


FIG.  20.     Granite  Bluff  shattered  by  Frost. 
(Minnesota  Geological  and  Natural  History  Survey.) 

this  way,  and  in  most  cases  these  soils  are  of  high  fertil- 
ity. The  action  of  water  is  not  alone  confined  to  form- 
ing soils  along  water  courses,  but  is  equally  prominent 
in  the  formation  of  soils  remote  from  streams  or  lakes, 
as  in  the  case  of  soils  deposited  by  glaciers. 

57.  Glacial  Action. —  At  one  time  in  the  earth's  history, 
the  ice  fields  of  polar  regions  covered  much  larger  areas 


58  SOILS   AND    FERTILIZERS 

than  at  present.20  Changes  of  climate  caused  a  recession 
of  these,  and  resulted  in  the  movement  of  large  bodies 
of  ice,  carrying  along  rocks  and  frozen  soil.  The  move- 
ment and  pressure  of  the  ice  pulverized  the  rock  and 
produced  soil.  This  action  is  well  illustrated  at  the 
present  time  where  mountains  rise  above  the  snow  line, 
and  the  ice  and  snow  melting  at  the  base  are  replaced  by 
ice  and  snow  from  farther  up,  moving  down  the  side  of 
the  mountain  and  carrying  along  crushed  stones  and 
soil.  King  estimates  that  an  ice  sheet  IO  feet  in  depth 
exerts  a  pressure  of  570  pounds  to  the  square  foot.  The 
frozen  mass  contains  boulders,  gravel,  and  sand  which 
act  as  a  grinding  plate  upon  the  rocky  surfaces  with 
which  it  comes  in  contact.15  The  rubbing  of  these  two 
surfaces  against  each  other  under  pressure  for  cen- 
turies has  resulted  in  the  production  of  vast  areas  of 
drift  soil. 

When  the  glacier  receded,  stranded  ice  masses  were 
distributed  over  the  land.  These  melted  slowly  and  by 
their  grinding  action  hollowed  out  places  some  of  which 
finally  became  lakes.  The  numerous  lakes  at  the  source 
of  the  Mississippi  River  are  supposed  to  have  been 
formed  by  glacial  action.  The  terminal  of  a  glacier  is 
called  a  moraine  and  is  covered  with  large  boulders 
which  have  not  been  disintegrated.  The  course  of  a 
glacier  is  frequently  traced  by  the  markings  or  scratches 
of  the  mass  on  rock  ledges.  In  glacial  soils,  the  rocks 
are  never  angular,  but  are  smooth  because  of  the  grind- 


GEOLOGICAL  STUDY  OF  SOILS  59 

ing  action  during  transportation.  The  area  of  glacial 
soils  in  the  northern  portion  of  the  United  States  is 
quite  large.  These  soils  are,  as  a  rule,  fertile  because  of 
the  pulverization  and  mixing  of  a  great  variety  of  rock. 

58.  Chemical  Action  of  Water.  —  The  chemical  action 
of  water  is  an  important  factor  in  soil  formation.  While 
nearly  all  rocks  are  practically  insoluble  in  water  there 
is  always  some  material  dissolved,  evidenced  by  the  fact 
that  all  spring  water  contains  dissolved  mineral  matter. 
When  charged  with  carbon  dioxide  and  other  gases, 
water  acts  as  a  solvent  upon  rocks ;  it  converts  many 
oxides,  as  ferrous  oxide,  into  hydroxides,  and  produces 
new  compounds  more  soluble  or  readily  disintegrated, 
as  deposits  of  clay,  which  have  been  formed  from  feld- 
spar rock  by  the  chemical  and  physical  action  of  water. 
Rock  decay  is  often  dependent  upon  chemical  change ; 
the  addition  of  water,  or  hydration  of  the  molecule,  par- 
ticularly of  the  silicates,  is  one  of  the  most  important 
chemical  changes.  When  rocks,  as  feldspar,  disinte- 
grate, there  is  an  addition  of  12  to  14  per  cent  of  water 
of  hydration  to  the  disintegrated  products.  This  chem- 
ical union  of  water  with  the  rock  materials  entirely 
changes  their  properties  and  often  prepares  the  way 
for  other  chemical  changes.  Water  takes  as  prominent 
a  part  in  the  decay  of  rocks  as  in  the  decay  of  vegeta- 
ble matter.  Dissolved  minerals  produce  many  chemical 
changes  in  both  rocks  and  soils.  The  chemical  action 
of  fertilizers,  known  as  fixation,  can  take  place  only 


6O  SOILS    AND    FERTILIZERS 

when  the  substances  are  in  solution.  In  fact,  water  is 
necessary  for  nearly  all  the  chemical  reactions  in  the 
soil  which  result  in  rendering  plant  food  available. 

59.  Joint  Action  of  Air  and  Gases.  —  In  the  disintegra- 
tion of  materials  to  form  soil,  air  takes  a  prominent 
part.     By  the  aid  of  oxygen,  carbon  dioxide,  and  other 
gases  and  vapors  in  the  air,  rock  disintegration  is  has- 
tened.    The  action  of  oxygen  changes  the  lower  oxides 
to  higher  forms.    All  rock  contains  more  or  less  oxygen 
in  chemical  combination.     The  carbon  dioxide  of  the  air 
under  some  conditions  favors  the  formation  of  carbon- 
ates.    The  disintegrating  action  of  air,  moisture,  and 
frost  is  illustrated  in  the  case  of  building  stones  which 
in  time   crumble  and  form   a   powder.     Many  of   the 
benefits  of  cultivation  are  due  to  aeration  of  the  soil,  as 
air  promotes   chemical  changes  of  mineral  substances 
and  prepares  the  way  for  life  processes  in  the  soil. 

60.  Action    of    Micro-organisms.  —  Micro-organisms, 
found  on  the  surface  and  in  the  crevices  of  rocks,  are 
active  agents  in  bringing  about  rock  decay,  deriving  all 
of  their  energy  from  the  chemical  changes  which  they 
induce  between  minerals,  and   obtaining  their  carbon 
from    the    air.     Such    organisms    incorporate    organic 
matter   with    the   rock   residues.21      Certain   nitrifying 
organisms  can  obtain  their  nitrogen  also  from  the  air, 
and  it  is  believed  that  they  have  largely  prepared  the 
way  for  the  production  of  agricultural  plants,  by  incor- 


GEOLOGICAL    STUDY    OF    SOILS  6 1 

porating  the  initial  stores  of  carbon  and  nitrogen  of  the 
air  with  the  disintegrated  rock  materials. 

61.  Action  of  Vegetation.  —  Some  of  the  lower  forms 
of  plants,  as  lichens,  do  not  require  soil  for  growth,  but 
are   capable   of   living   on   the  bare  surface  of  rocks, 
obtaining   food   from    the   air,    and   leaving   a   certain 
amount  of  vegetable  matter  which  undergoes  decay  and 
is  incorporated  with  the  rock  particles,  preparing  the 
way  for  higher  orders  of  plants  which  take  their  food 
from  the  soil.     When  this  vegetable  matter  decays,  it 
enters  into  chemical  combination  with   the  pulverized 
rock,  forming  humates.18     The  disintegrating  action  of 
plant  roots  and  vegetable  matter  upon  rocks  has  been 
an  important  factor  in  soil  formation.     The  action  of 
vegetable   remains   in   soil   production  is   discussed  in 
Chapter  III. 

62.  Earthworms.  —  Many    soils    have    been    greatly 
modified  by   the   action   of   earthworms.     The  soil   in 
passing  through  their  digestive  tract  is  ground  into  finer 
particles  and  is  intimately  mixed  with  the  indigestible 
matter  excreted  by  the  worms.    In  the  case  of  rich  loam 
soils   it  is  estimated  that  all  of  the  particles  have  at 
some  time  passed  through  the  digestive  tract  of  earth- 
worms.    JVhere  they  have  been  active,  air  and  water 
are  admitted  into  the  soil  more  readily.     The  action  of 
earthworms    in    soils  has  been  extensively  studied  by 
Darwin. 


62  SOILS   AND   FERTILIZERS 

63.  Wind. — Wind  also  has  been  an  important  factor 
in  the  production  and  modification  of  soils.    The  denud- 
ing   effects   of    heavy   wind   storms   are   well   known. 
Large  areas  of  wind-formed  soils  are  found   in  some 
countries.     Sand  dunes  are  transported  by  winds,  and 
often  their  subjugation  by  soil-binding  plants  is  neces- 
sary in  order  to  prevent  encroachment  upon  valuable 
farm  lands  and  inundation  of  villages.     Soils  formed  by 
the  action  of  winds  are  called  aeolian  soils. 

64.  Combined  Action  of  the  Various  Agents.  —  In  the 
decay  of  rocks  the  various  agents  named  —  water  act- 
ing  mechanically  and  chemically,  heat  and  cold,  air, 
micro-organisms,  vegetation,  earthworms,  and  wind  — 
have  acted  jointly,  and  have  produced  more  rapid  disin- 
tegration than  if  each  agent  had  acted  separately. 

DISTRIBUTION  OF   SOILS 

65.  Sedentary   and   Transported   Soils.  —  The    place 
which  a  soil  occupies  is  not  necessarily  where  it  was 
formed ;  that  is,  a  soil  may  be  produced  in  one  locality 
and  transported  to  another.     Soils  are  either  sedentary 
or  transported.     Sedentary  soils  are  those  which  occupy 
the  original  position  where  they  were  formed.     They 
usually   have   but   little   depth   before  rock  §urface  is 
reached.     The  stones  in  such  soils,  except  where  modi- 
fied by  weathering,   have  sharp  angles  because  they 
have  not  been  ground  by  transportation.     In  the  south- 


GEOLOGICAL  STUDY  OF  SOILS  63 

ern  part  of  the  United  States,  east  of  the  Mississippi 
River,  there  are  large  areas  of  sedentary  soils  as  fer- 
rogenous  clays  in  an  advanced  state  of  decay. 

Transported  soils  are  those  which  have  been  formed 


FIG.   22.    A  Boulder-filled  Channel. 
(Minnesota  Geological  and  Natural  History  Survey.) 

in  one  locality  and  carried  by  various  agents  as  gla- 
ciers, rivers,  or  winds  to  other  localities,  the  angles  of 
the  stones  in  these  soils  having  been  ground  off  during 
transportation.  Transported  soils  are  divided  into 
classes  according  to  the  ways  in  which  they  have  been 
formed ;  as  drift  soils  produced  by  glaciers,  alluvial  soils 
by  rivers  and  lakes,  seolian  soils  by  winds,  and  colluvial 
soils  formed  of  rocks  and  debris  from  mountain  sides. 


64  SOILS    AND    FERTILIZERS 

In  some  localities  volcanic  soils  are  found.  They  are 
extremely  varied  in  texture  and  composition;  some  are 
very  fertile  and  contain  liberal  amounts  of  alkaline  salts 
and  phosphates,  while  others  contain  so  little  plant  food 
that  they  are  sterile. 

ROCKS  AND  MINERALS  FROM  WHICH  SOILS  ARE 
FORMED 

66.  Composition  of  Rocks.  —  Rocks  are  composed  of 
either  a  single  mineral  or  of  a  combination  of  minerals. 
Most   of  the   common  minerals   are   definite    chemical 
compounds  and   have  a  varied    range  in  composition, 
due  to  the  fact  that  one  element  or  compound  may  be 
partially  or  entirely  replaced  by  another.     Most  rocks 
from  which  soils  have  been  derived  contain  minerals,  as 
feldspar,  mica,  hornblende,  and  quartz. 

67.  Quartz. — Quartz  is  the  principal  constituent  of 
many  rock  formations.     Pure  quartz  is  silicic  anhydride, 
SiO2,  and  a  soil  formed  from  pure  quartz  alone  would 
be  sterile.     White  sand  is  nearly  pure  quartz  or  silica. 
Silica   enters   into    combination    with    many   elements, 
forming  a  large  number  of  minerals.     Particles  of  quartz 
when   cemented  with  iron  compounds  form  sandstone 
rock.     Sand  is  derived  mainly  from  the  decay  of  rocks 
containing  quartz. 


M/UbAUUUK    UlUUUb« 

68.    Feldspar   is    composed    of    silica,    alumina,    a 
potash  or  soda.     Lime  may  also  be  present,  and  reph 


and 
[ace 


GEOLOGICAL  STUDY  OF  SOILS  6$ 

a  part  or  nearly  all  of  the  soda.  If  the  mineral  contains 
soda  as  the  alkaline  constituent,  it  is  known  as  albite, 
or  if  mainly  potash,  it  is  called  potash  feldspar  or 
orthoclase. 

The  members  of  the  feldspar  group  are  insoluble  in 
acids,  and  before  disintegration  takes  place  are  not 
capable  of  supplying  plant  food.  Potash  feldspar  con- 
tains from  12  to  15  per  cent  of  potash,  none  of  which  is 
of  value  as  plant  food  until  disintegrated.  When  feld- 
spar undergoes  disintegration,  it  produces  kaolin  or  clay. 
A  soil  formed  from  feldspar  is  usually  well  stocked  with 
potash.  Feldspar  containing  lime  readily  yields  to  the 
solvent  action  of  water  in  which  there  is  carbon  dioxide. 

Orthoclase,  AlKSi3O8 Potash  feldspar 

Albite,         AlNaSi3O8 Sodium  feldspar 

69.  Hornblende.  — The  hornblende  and  augite  groups 
are  formed  by  the  union  of  magnesium,  calcium,  iron, 
and  manganese,  with  silica.  As  a  rule  none  of  the 
members  of  the  alkali  family  are  present  in  hornblende. 
The  augites  are  double  silicates  of  iron,  manganese,  cal- 
cium, and  magnesium.  Quite  frequently,  phosphoric 
acid  is  in  chemical  combination  with  the  iron.  The 
members  of  this  group  are  readily  distinguished  by 
their  color,  which  is  black,  brown,  or  brownish  green. 
The  hornblendes  which  contain  lime  are  quite  readily 
decomposed  when  subjected  to  weathering  and  the 
action  of  water  charged  with  carbon  dioxide.  They  are 


66  SOILS    AND    FERTILIZERS 

mainly  insoluble  in  acids,  and  do  not  as  a  rule  form 
very  fertile  soils. 

70.  Mica.  —  Mica  is   quite   complex  in  composition, 
is  an  abundant  mineral,  and  is  composed  of  silica,  iron, 
alumina,  manganese,  calcium,   magnesium,    and    potas- 
sium.    Mica  is  a  polysilicate.     The  color  may  be  white, 
brown,  black,  or  bluish  green,  owing  either  to  the  ab- 
sence of   iron,  or  to  its  presence  in  various  amounts. 
The  chief  physical  characteristic  of  the  members  of  this 
group  is  the  ease  with  which  they  are  split  into  thin 
layers.     It  is  to  be  observed  that  the  mica  group  con- 
tains all  the  elements  of  both  feldspar  and  hornblende. 
Mica  is  quite  resistant  to  chemical  change. 

Soils  formed  from  thoroughly  disintegrated  mica  are 
usually  fertile,  owing  to  the  variety  of  essential  elements 
present. 

71.  Granite   is    composed   of    quartz,   feldspar,   and 
mica.     It  is  a  very  hard  rock  and  slow  to  disintegrate. 
The  different  shades  of  granite  depend  upon  the  pro- 
portion  in   which   the   various   minerals    are    present. 
Inasmuch  as  it  contains  so  many  minerals,  it  usually 
follows  that  granite  soil  is  fertile ;  although  when  not  com- 
pletely disintegrated  or  when  disintegrated  and  leached, 
it  is  unproductive.     Pure  powdered  granite  before  un- 
dergoing disintegration  furnishes  but  little  plant  food. 
After  weathering,   the   plant  food  gradually  becomes 
available.     Granite  varies  in  both  physical  and  chemi- 


GEOLOGICAL    STUDY   OF    SOILS  6? 

cal  composition,  and  some  disintegrates  more  readily 
than  others.  Gneiss  belongs  to  the  granite  series,  but 
differs  from  true  granite  in  containing  a  large  amount 
of  mica.  Mica  schist  contains  a  larger  amount  of  mica 
than  gneiss. 

72.  Zeolites.  — The  zeolites  are  a  large  group  of  sec- 
ondary or  derivative  minerals  formed  from  disintegrated 
rock.      They  are  polysilicates  containing  alumina  and 
members  of  the  alkali  and  lime  families,  and  all  contain 
water  held  in  chemical  combination.     They  are  partially 
soluble  in  dilute  hydrochloric  acid  and  belong  to  that  class 
of  compounds  which  are  capable,  to  a  certain  extent,  of 
becoming  available  as  plant  food.   In  color,  they  are  white, 
gray,  or  red.     Zeolites  are  quite  abundant  in  clay  and  are 
an  important  factor  in  soil  fertility.      It  is  this  group  of 
hydrated  silicates  which  takes  such  an  important  part  in 
the  process  of  fixation.     The  zeolites,  when  disintegrated, 
particularly  by  glacial  action,  form  very  fertile  soils. 

73.  Apatite  or  Phosphate   Rock.  —  Apatite   is   com- 
posed mainly  of  phosphate  of  lime,  Ca3(PO4)2,  together 
with  small  amounts  of  other  compounds,  as  fluorides 
and   chlorides.     It  is  generally  of  a  green  or  yellow 
color  and  is  present  in  many  soils,  but  is  of  little  value 
as  plant  food  unless  associated  with  organic  matter  and 
soluble  alkaline  salts. 

74.  Kaolin  is  chemically  pure  clay  and  is  formed  by 
the  disintegration  of  feldspar.     When  feldspar  is  de- 


68  SOILS    AND    FERTILIZERS 

composed  and  acted  upon  by  water,  the  potash  is  re- 
moved and  water  of  hydration  is  taken  up,  forming  the 
product  kaolin,  which  is  hydrated  silicate  of  alumina, 
Al4(SiO4)g .  H2O.  Impure  varieties  of  clay  are  colored 
red  and  yellow  owing  to  the  presence  of  iron  and 
other  impurities.  Pure  kaolin  is  white,  is  insoluble  in 
acids,  and  is  incapable  of  supplying  any  nourishment  to 
plants.  Clay  soils  are  fertile  on  account  of  the  other 
minerals  and  organic  matter  mixed  with  the  clay  and  are 
usually  well  stocked  with  potash  because  of  its  incom- 
plete removal  from  the  disintegrated  feldspar.  It  is  to 
be  observed  that  the  term  '  clay '  used  chemically  means 
aluminum  silicate,  while  physically  it  is  any  substance 
the  particles  of  which  are  less  than  0.005  mm.  in  diameter. 

75.  Limestone. — Limestone  is  present  in  many  sec- 
ondary rocks.    It  is  composed  of  calcium  carbonate  and 
is   slowly  soluble  in  water  containing  carbon  dioxide. 
Extensive  deposits  of  calcium  carbonate,  as  limestone, 
marble,  and  chalk,  occur  in  nature.     It  is  widely  dif- 
fused in  soils,  and  is  a  constituent  that  imparts  fertility. 
Many  soils  contain  appreciable  amounts  of  disintegrated 
limestone. 

76.  Disintegration  of  Rocks  and  Minerals.  —  In  ad- 
dition to    the   rocks    and    minerals   which    have    been 
mentioned,  there  are  many  others  that  contribute  to  soil 
formation,  as  glauconite,  a  hydrated  silicate  of   iron ; 
alumina  and    potash;    limonite,   a   hydrated   oxide   of 


GEOLOGICAL    STUDY   OF    SOILS 


iron ;  dolomite,  a  double  carbonate  of  calcium  and  mag- 
nesium; serpentine,  a  silicate  of  magnesium;  and  gypsum 
calcium  sulphate.  All  rocks  and  minerals  are  subject  to 
disintegration  and  change  in  chemical  composition  and 
physical  properties.  The  process  of  soil  formation  has 
resulted  in  numerous  chemical  and  physical  changes. 
These  changes  are  still  taking  place,  and  as  a  result 
plant  food  is  constantly  being  made  available. 

CHEMICAL  COMPOSITION  OF  ROCKS" 


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77.  Value  of  Geological  Study  of  Soils.  —  Agricul- 
tural geology  is  a  valuable  aid  in  studying  soil  prob- 
lems, but  like  other  sciences  it  is  incapable  alone  of 
solving  all  the  problems  of  soil  fertility.  Means  have 
not  yet  been  devised  for  accurately  determining  the 
extent  of  rock  disintegration  and  the  rapidity  with 
which  it  has  taken  place  or  the  degree  to  which  dis- 


7<D  SOILS   AND    FERTILIZERS 

integrated  minerals  have  been  removed  from  rocks  by 
leaching  and  other  agencies.  It  is  known  that  the 
rate  of  weathering  of  soils  is  influenced  by  various  fac- 
tors, as  origin,  texture,  composition,  humidity  and  other 
climatic  conditions,  presence  of  decaying  organic  matter, 
micro-organisms,  mechanical  treatment  and  manipula- 
tion of  the  soil,  fertilizers,  sunlight  and  vegetation. 
Some  of  these  agencies  for  promoting  soil  disintegra- 
tion are  under  the  control  of  the  farmer  and  are  utilized 
by  him  in  rendering  plant  food  available.  A  knowledge 
of  the  origin  of  soils,  of  the  minerals  of  which  they  are 
composed,  and  of  the  ways  in  which  they  have  been 
distributed  is  of  much  assistance  in  determining  their 
agricultural  value. 


78.  Elements  Present  in  Soils.  —  Physically  consid- 
ered, a  soil  is  composed  of  disintegrated  rock  mixed 
with    animal    and  vegetable   matter;    chemically   con- 
sidered, the  rock  particles  consist  of  a  large  number  of 
simple  and  complex  compounds,  each  compound  being 
composed   of   elements    chemically   united.     Elements 
unite  to  form  compounds,  compounds  to  form  minerals, 
minerals  to  form  rocks,  and  disintegrated  rock  forms 
soil.     When  rocks  decompose,  the  disintegration,  except 
in  a  few  cases,  is  never  carried  to  the  extent  of  liberating 
the  elements,  but  the  process  ceases  when  the  minerals 
have  been  broken  up  into  compounds.     While  there  are 
present  in  the  crust  of  the  earth  between  65  and  70 
elements,  only  about  15  are  found  in  animal  and  plant 
bodies,  and  of  these  but  12  are  known  to  be  absolutely 
essential.     Only  four  of  the  elements  which  are  of  most 
importance  are  at   all  liable   to  be   deficient  in   soils. 
These  four  elements  are :  nitrogen,  phosphorus,  potas- 
sium, and  calcium. 

79.  Classification   of  the   Elements.  —  The   elements 
found  most  abundantly  in  soils  are   divided  into  two 
classes : 

7* 


72  SOILS    AND    FERTILIZERS 

ACID-FORMING  ELEMENTS  BASE-FORMING  ELEMENTS 

""Oxygen O      Aluminum Al 

Silicon Si     "Potassium K 

-Phosphorus P      Sodium Na 

*  Sulphur S    'Calcium Ca 

Chlorine Cl     -Magnesium Mg 

"Nitrogen N     Jron Fe 

Hydrogen H 

Carbon C 

Boron,  fluorine,  manganese,  and  barium  are  usually 
present  in  small  amounts,  besides  others  which  may  be 
found  in  traces,  as  the  rare  elements  lithium  and 
titanium. 

For  crop  purposes  the  elements  of  the  soil  may  be 
divided  into  three  classes  : 

1.  Essential  elements   most  liable   to   be   deficient; 
nitrogen,  potassium,  phosphorus,  and  calcium. 

2.  Essential  elements   usually  abundant;  iron,  mag- 
nesium, and  sulphur. 

3.  Unnecessary    and    accidental    elements,    usually 
abundant;    as   chlorine,    silicon,    aluminum,    and   man- 
ganese. 

80.  Combination  of  Elements.  —  In  dealing  with  the 
composition  of  soils,  the  percentage  amounts  of  the 
individual  elements  are  not  given,  except  in  the  case  of 
nitrogen,  but  instead,  the  amounts  of  the  correspond- 
ing oxides.  The  elements  do  not  exist  in  a  free  state 
in  soils,  but  are  combined  with  oxygen  and  other 
elements  to  form  compounds.  When  considered  as 


THE    CHEMICAL    COMPOSITION    OF    SOILS 


73 


oxides,  the  acid  and  basic  constituents  may  form  various 
compounds  as: 


Calcium 


Potassium     .  . 
Sodium    . 

Magnesium  .  . 

Iron     .     .     .  . 


Silicate 

Phosphate 

Chloride 

Sulphate 

Carbonate 


The  following  reactions  will  explain  some  of  the  more 
elementary  combinations  : 


SiO2  =  CaSiO3 


CaO 

3CaO  +  P2O5  =  Ca3(PO4)2 
CaO  +  SO3   =  CaSO4 
CaO  +  CO2   =  CaCO3 


CaO 


K2O 


N2O5  =  Ca(NO3)2 
SO3  =  K2SO4 
Na2O  4-  SO3    =  Na2SO4 
MgO  +  SO3  =  MgSO4 


It  is  often  difficult  to  determine  with  accuracy  the 
exact  form  or  combination  in  which  an  element  is 
present  in  the  soil.  When  reported  as  the  oxide,  bases 
may  be  considered  as  combined  with  any  of  the  ox- 
ides of  the  acid-forming  elements,  as  indicated  by 
the  reactions,  to  form  salts.  Each  compound  of 
an  element  may  have  a  different  value  as  plant  food, 
hence  it  is  important  to  determine  as  far  as  possible 
the  form  or  solubility  of  the  various  elements  of  plant 
food. 


74  SOILS    AND    FERTILIZERS 

ACID-FORMING  ELEMENTS 

81.  Silicon.  —  The   element  silicon  makes  up  from 
a  quarter  to  a  third  of  the  solid  crust  of  the  earth  and 
next  to  oxygen  is  the  most  abundant  element  found  in 
soils.     Silicon  never  occurs  in  the  soil  in  the  free  state. 
It  either  combines  with  oxygen  to  form  silica  (SiO2),  or 
with  oxygen  and  some  base-forming  element  or  elements 
to  form  silicates.     Silica  and  the  various  silicates  are 
by  far  the  most  abundant  compounds  present  in  the 
soil.     Silicon   is   not   one   of   the    elements   absolutely 
necessary  for  plant  growth,  and  even  if  it  were,  all  soils 
are  so  abundantly  supplied  that  it  would  not  be  necessary 
to  use  it  in  fertilizers. 

When  two  or  more  base-forming  elements  are  united 
with  the  silicate  radical,  a  double  silicate  results.  The 
double  silicates  are  the  most  common  compounds 
present  in  soils.  There  are  also  a  number  of  forms  of 
silicic  acid  which  greatly  increase  the  number  of  sili- 
cates, and  a  study  of  the  composition  of  soils  is  largely 
a  study  of  these  various  silicates. 

82.  Carbon  is  an  .acid-forming  element  and  belongs  to 
the  same  family  as  silicon.     It  is  found  in  the  soil  as 
one  of  the  main  constituents  of  the  volatile  or  organic 
compounds,  and  also  unites  with  oxygen  and  the  base- 
forming    elements,    producing   carbonates,    as   calcium 
carbonate  or  limestone.     The  carbon  of  the  soil  takes 
no  direct   part   in   forming  the  carbon  compounds  of 


THE    CHEMICAL    COMPOSITION    OF    SOILS  75 

plants.  It  is  not  necessary  to  apply  carbon  fertilizers 
to  produce  the  carbon  compounds  of  plants,  because 
the  carbon  dioxide  of  the  air  is  the  source  for  crop 
production.  It  is  estimated  that  there  are  30  tons 
of  carbon  dioxide  in  the  air  over  every  acre  of  the 
earth's  surface.22  The  carbon  in  the  soil  is  an  indirect 
element  of  fertility,  because  it  is  usually  combined  with 
other  elements,  as  nitrogen  and  phosphorus,  which  are 
absolutely  necessary  for  crop  growth. 

83.  Sulphur  occurs  in  all  soils  mainly  in  the  form  of 
sulphates,  as   calcium    sulphate,   magnesium    sulphate, 
and   sodium   sulphate.     It  is  an  essential   element  of 
plant  food.     There  is  generally  less  than  o.io  per  cent 
of  sulphuric  anhydride  in  ordinary  soils,  but  the  amount 
required  by  crops   is   small   and   there   is   usually   an 
abundance. 

84.  Chlorine  is  found  in  all  soils,  generally  in  com- 
bination with  sodium,  as  sodium  chloride.     It  may  be 
in  combination  with  other  bases.     Soils  which  contain 
more  than  0.2  per  cent  are,  as  a  rule,  sterile.     Chlorine 
is  present  in  the  soil  in  soluble  forms.     It  occurs  in  all 
plants  but  is  not  absolutely  necessary  for  plant  growth. 
Its  use  in  fertilizers  is  unnecessary,  although  chlorine 
with  sodium,  as  common  salt,  is  sometimes  used  as  an 
indirect  fertilizer. 

85.  Phosphorus,   one  of   the  essential   elements  for 
plant  growth,  is  combined  with  both  the  volatile  and 


76  SOILS    AND    FERTILIZERS 

non-volatile  elements  of  the  soil.  Plants  cannot  make 
use  of  it  in  other  forms  than  the  phosphates.  Phos- 
phorus is  usually  present  in  the  soil  as  calcium  phos- 
phate, magnesium  phosphate,  or  aluminum  phosphate, 
and  may  also  be  combined  with  the  humus,  forming 
humic  phosphates.  The  form  of  the  phosphates,  as 
available  or  unavailable,  is  an  important  factor  in  soil 
fertility.  Soils  are  quite  liable  to  be  deficient  in  phos- 
phates, inasmuch  as  they  are  so  largely  drawn  upon 
by  many  crops,  particularly  grain  crops,  where  the 
phosphates  accumulate  in  the  seed,  and  are  sold  from 
the  farm.  The  phosphorus  content  of  soils  is  usually 
reported  as  phosphorus  pentoxide  (P2O5),  anhydrous 
phosphoric  acid,  commonly  called  phosphoric  acid. 

86.  Nitrogen.  —  This  element  is  present  in  soils  in 
various  forms.  As  a  mineral  constituent  it  is  combined 
with  oxygen  and  the  base-forming  elements  as  potas- 
sium, sodium,  and  calcium,  forming  nitrates  and  nitrites, 
which,  on  account  of  their  solubility,  are  never  found 
in  average  soils  in  large  amounts.  Nitrogen  is  mainly 
in  organic  combination,  being  associated  with  carbon, 
hydrogen,  and  oxygen  as  one  of  the  elements  form- 
ing the  organic  matter  of  soils.  Nitrogen  may  also 
be  present  in  small  amounts  in  the  form  of  ammonia,  or 
of  ammonium  salts,  derived  from  rain  water  and  from 
the  decay  of  vegetable  and  animal  matter.  While  free 
nitrogen  is  in  the  air  in  large  amounts,  it  can  be  ap- 
propriated as  food  in  this  form  by  only  a  limited  num- 


THE    CHEMICAL    COMPOSITION    OF    SOILS  ?/ 

her  of  plants  and  by  them  indirectly.  For  ordinary 
agricultural  crops,  particularly  the  cereals,  nitrogen 
must  be  present  in  the  soil  as  combined  nitrogen.  This 
is  the  most  expensive  of  any  of  the  elements  of  plant 
food,  and  is  liable  to  be  deficient.  No  other  element 
takes  such  an  important  part  in  agriculture  or  in  life 
processes  as  does  nitrogen. 

87.  Oxygen. —  Oxygen   is   combined   with   both   the 
acid-  and  base-forming  elements  and  is  found  in  nearly 
all  of  the  compounds  of  the  soil.     It  has  been  estimated 
that  about  one  half  of  the  crust  of  the  earth  is  com- 
posed of  oxygen,  which  in  large  amounts  is  combined 
with  silicon,    forming   silica.     That  which   is   held   in 
chemical  combination  in  the  soil  takes  no  part  in  the 
formation  of  plant  tissue.     In  addition  to  being  present 
in  the  soil,  oxygen  constitutes  eight  ninths  of  the  weight 
of  water  and  about  one  fifth  of  the  weight  of  air.     It 
also  forms  about  50  per  cent  of  the  compounds  found 
in  plants  and  animals.     Oxygen  in  the  interstices  of  the 
soil  is  an  active  agent  in  bringing  about  many  chemical 
changes,  as  oxidation  of  the  organic  matter,  and  disin- 
tegration of  the  soil  particles. 

88.  Hydrogen.  —  This  element  is  never  found  in  a 
free  state  in  the  soil,  but  is  combined  with  carbon  and 
oxygen  in  animal  and  vegetable  matter,  with  oxygen  to 
form  water,  and  in  a  few  cases  with  some  of  the  base 
elements  to  form  hydroxides.     It  is  not  in  the  soil  in 


78  SOILS   AND   FERTILIZERS 

large  amounts,  and  that  which  forms  a  part  of  the 
tissues  of  plants  and  animals  comes  from  the  hydrogen 
in  water.  Hydrogen  in  the  organic  matter  of  soils  takes 
no  part  directly  in  producing  the  hydrogen  compounds 
of  plants.  On  account  of  its  lightness,  hydrogen  never 
makes  up  a  very  large  proportion,  by  weight,  of  the 
composition  of  bodies. 

BASE-FORMING  ELEMENTS 

89.  Aluminum  is  present  in  the  soil  in  the  largest 
amount  of  any  of  the  base  elements.     It  forms  probably 
from   6  to  10  per  cent  of  the  solid  crust  of  the  earth. 
As  previously  stated  aluminum  is  one  of  the  constituents 
of  clay,  and  is  not  necessary  for  plant  growth.     Physi- 
cally, however,  the  aluminum  compounds  take  an  im- 
portant part  in  soil  fertility.     Aluminum  is  usually  in 
combination  with  silica  or  with  silica  and  some  base- 
forming  element,  as  iron,  potassium,   or  sodium.     The 
various  forms  of  aluminum  silicate  are  the  most  numer- 
ous compounds  found  in  soils.     Alumina  is  the  oxide  of 
aluminum,  A12O3,  and  is  the  usual  form  in  which  this 
element  is  reported  in  soil  and  rock  analyses. 

90.  Potassium  is  in  the  soil  mainly  in  the  form  of 
silicates,  and  is  one  of  the  elements  absolutely  necessary 
for  plant  growth.     The  term  'potash'  (potassium  oxide, 
K2O)  is  usually  employed  when  reference  is  made  to 
the  potassium  compounds.     The  amount  and  form  of 


THE    CHEMICAL    COMPOSITION   OF   SOILS  79 

the  soil  potash  have  an  important  bearing  upon  fertility. 
Potassium  is  one  of  the  three  elements  of  plant  food 
usually  supplied  in  fertilizers.  The  form  in  which  it  is 
in  the  soil  and  its  economic  supply  as  plant  food  are 
important  factors  in  crop  production.  The  amount  of 
potash  in  soils  ranges  from  0.02  to  0.8  per  cent  In  a 
fertile  soil  it  rarely  falls  below  0.2  per  cent. 

91.  Calcium  is  in  the  soil  in  a  variety  of  forms,  as 
calcium  carbonate,  calcium   silicate,  calcium   sulphate, 
and  calcium  phosphate.     The  calcium  oxide,  CaO,  of 
the  soil  is  generally  spoken   of  as  the  lime  content. 
Calcium  carbonate  and  sulphate  are  important  factors 
in  imparting  fertility.     A  subsoil  with  a  good  supply  of 
lime  will  stand  heavy  cropping  and  remain  in  excellent 
chemical  and  physical  condition  for  crop  growth.     In  a 
good  soil  there  is  usually  0.2  per  cent  or  more  of  lime, 
mainly  as  calcium  carbonate. 

92.  Magnesium  is  found  in  all  soils  and  is  usually 
associated  with  calcium,  forming  the  mineral  dolomite, 
which  is  a  double  carbonate  of  calcium  and  magnesium. 
Magnesium  may  also  be  present  in  the  soil  in  the  form 
of   magnesium  sulphate  or  magnesium  chloride.      All 
crops  require  a  certain  amount  of   magnesia  in  some 
form,  in  order  to  reach  maturity  and  produce  fertile 
seeds.     There  is  generally  in  all  soils  an  amount  suffi- 
cient for  crop  purposes,  hence  it  is  not  necessary  to 
consider    this   element   in   connection   with   fertilizers. 


8O  SOILS   AND    FERTILIZERS 

The  term  'magnesia'  (magnesium  oxide,  MgO)  is  used 
when  reference  is  made  to  the  magnesium  compounds 
of  the  soil. 

93.  Sodium  is  in  the  soil  mainly  as  sodium  silicate, 
and  to  about  the  same  extent  as  potassium,  which  it 
resembles  chemically  in  many  ways.     It  cannot,  how- 
ever, replace  potassium  in  plant  growth.     Inasmuch  as 
sodium  takes  an  indifferent  part  in  plant  nutrition,  it 
is  never  used  as  a  fertilizer  except  in  an  indirect  way. 

94.  Iron  is  an  element  necessary  for  plant  food  and  is 
found  in  all  soils  to  the  extent  of  from  i  to  4  per  cent. 
Crops  require  only  a  small  amount  of  iron,  hence  there 
is  always  sufficient  for  crop  purposes.     Iron  in  soils  is 
in  the  form  of  oxides,  hydroxides,  and  silicates. 

FORMS  OF  PLANT  FOOD 

95.  Three  Classes  of  Compounds.  —  For  agricultural 
purposes,  the  compounds  present  in  soils  may  be  divided 
into  three  classes  :9  (i)  Compounds  soluble  in  water  and 
dilute  organic  and  mineral  acids ;  (2)  compounds  soluble 
in  more  concentrated  acids ;   (3)  insoluble  compounds 
decomposed  by  strong  acids  and  fluxes. 

96.  Water-  and  Dilute  Acid-soluble  Matter  of  Soils.  — 
This  class  includes  silicates  and  other  compounds  of 
potash,  soda,  lime,  magnesia,  phosphorus,  etc.,  which  are 


THE    CHEMICAL    COMPOSITION   OF    SOILS 


8l 


soluble  in  the  soil  water  and  in  very  dilute  organic  and 
mineral  acids,  and  represents  the  most  soluble  and  the 

most  active  and  valuable 
forms  of  plant  food.  There 
is  only  a  very  small  amount 
in  these  forms.  In  100 
pounds  of  arable  soil,  rarely 
more  than  0.005  pound  of 
any  one  of  the  important 
elements  is  soluble  in  the 
soil  water  or  more  than  0.05 
pound  in  dilute  organic  acids. 


97.  Acid-soluble  Matter  of 
Soils.  —  The  plant  food  of 
the  second  class  is  in  a  some- 
what more  insoluble  form, 
and  consists  of  compounds, 
principally  the  zeolites,  sol- 
uble in  hydrochloric  acid  of 
23  per  cent  strength,  sp.  gr. 
1.115.  This  represents  the 
limit  of  the  solvent  action 
of  the  roots  of  plants.9  In 
this  class  are  included  also 
all  the  mineral  elements 
combined  with  the  humus  and  soluble  in  dilute  alkalies. 
As  a  rule,  not  over  10  to  20  per  cent  of  the  total  soil  is 
soluble  in  hydrochloric  acid;  and  the  more  important 


FIG.  23.    Oat  Plant  grown  in  soil 
extracted  with  hydrochloric  acid. 


82  SOILS   AND   FERTILIZERS 

elements  make  up  only  a  small  part  of  this  amount  In 
200  samples  of  soil,  the  potash,  nitrogen,  lime,  magnesia, 
and  phosphoric  and  sulphuric  anhydrides  amounted  to 
3.5  per  cent ;  in  many  fertile  soils  the  sum  of  these  is  less 
than  1.50  per  cent.  This  means  that  in  every  100  pounds 
of  soil  there  are  only  from  1.5  to  3.5  pounds  which  can 
take  any  active  part  in  the  support  of  a  crop,  while  96  to 
98.5  pounds  are  present  simply  as  so  much  inert  material, 
and  valuable  only  from  a  physical  point  of  view.  Not 
all  of  the  potash,  for  example,  soluble  in  hydrochloric 
acid  is  equally  valuable.  In  fact,  the  acid  represents 
more  than  the  limit  of  the  crop's  feeding  power,  when 
there  is  not  enough  of  more  soluble  forms  to  aid  in  the 
first  stages  of  growth. 

98.  Acid-insoluble  Matter  of  Soils.  —  This  class  in- 
cludes all  of  those  compounds  of  the  soil  which  require 
the  joint  action  of  the  highest  heat  and  the  strongest 
chemicals  in  order  to  decompose  them.  The  insoluble 
residue  obtained  after  digesting  a  soil  with  strong  hydro- 
chloric acid  contains  potash,  soda,  and  limited  amounts 
of  magnesia  and  phosphoric  acid,  with  other  elements 
which  are  of  no  immediate  value  as  plant  food.  When 
seed  was  planted  in  soil  extracted  with  strong  hydro- 
chloric acid,  it  made  no  growth  after  the  reserve  food  in 
the  seed  had  been  exhausted.  A  plant  grown  in  such 
a  soil  is  shown  in  the  illustration.84  (Fig.  23.) 

The  acid-insoluble  matter  of  soils  is  capable  of  under- 
going disintegration  and  in  time  may  be  changed  to  the 


THE    CHEMICAL    COMPOSITION    OF    SOILS  83 

second  or  zeolitic  class  of  silicates.  This  process,  how- 
ever, is  too  slow  to  be  relied  upon  as  an  immediate 
source  of  plant  food. 

In  the  following  table  are  given  the  percentage 
amounts  of  compounds  soluble  and  insoluble  in  hydro- 
chloric acid  for  a  few  typical  soils  :9 


WHEAT 
SOIL 

HEAVY  CLAY 
SOIL 

GRASS  AND 
GRAIN  SOIL 

Soluble 
inHCl 

Insol- 
uble 
residue 

Soluble 
inHCl 

Insol- 
uble 
residue 

Soluble 
inHCl 

Insol- 
uble 
residue 

Insoluble  matter      .     . 
Potash      

63.07 
0.54 
0.45 

2-44 

1.85 

4.18 

7.89 

0.38 

O.II 

84.77 
0.21 

O.22 
0.48 

o-34 
3-76 
6.26 

O.I2 
0.09 

84.08 
0.30 
0.25 
0.51 
0.26 
2.56 
2.99 
0.23 
0.08 

1-45 
0.25 

0-35 
0.46 
1.07 
9.72 
0.05 

O.O2 

2.18 

3-55 
0.36 
0.25 
0.78 
5-54 

0.24 

346 
2.95 

0.16 
0.47 
0.72 

5-44 
0.08 
0.25 

Soda    

Ljme    

Magnesia  

Iron     

Alumina    

Phosphoric  acid      .     . 
Sulphuric  acid    .     .     . 

The  insoluble  matter,  after  digestion  with  hydro- 
chloric acid,  was  submitted  to  fusion  analysis,  and  the 
figures  given  under  insoluble  residue  represent  the 
amounts  of  potash,  soda,  etc.,  insoluble  in  the  acid.  In 
the  clay  soil,  94  per  cent  of  the  total  potash  was  in 
forms  insoluble  in  hydrochloric  acid. 


99.   Soluble  and  Insoluble  Potash  and  Phosphoric  Acid. 
—  From  the  preceding  table  it  is  to  be  observed  that 


84  SOILS   AND    FERTILIZERS 

the  larger  portion  of  the  potash  in  the  soil  is  insoluble 
in  hydrochloric  acid.  A  soil  may  contain  from  2  to  3 
per  cent  of  total  potash,  and  90  per  cent  or  more  may  be 
in  such  firm  chemical  combination  with  aluminum,  sili- 
con, and  other  elements,  as  to  resist  the  solvent  action 
of  plant  roots.  The  larger  portion  of  the  phosphoric 
acid  of  the  soil  is  soluble  in  hydrochloric  acid.  In  some 
soils,  however,  from  20  to  40  per  cent  is  present  as  the 
third  class  of  compounds.  When  a  soil  is  digested  with 
hydrochloric  acid,  the  insoluble  residue  is  usually  a  fine 
gray  powder.  Some  clay  soils  retain  their  red  color 
even  after  treatment  with  acids,  showing  that  the  iron 
is  in  part  in  chemical  combination  with  the  more  com- 
plex silicates. 

In  order  to  decompose  the  insoluble  residue  obtained 
from  the  treatment  with  hydrochloric  acid,  fluxes,  as 
sodium  carbonate  and  calcium  carbonate,  are  employed 
which,  at  a  high  temperature,  act  upon  the  complex  sili- 
cates and  produce  silicates  soluble  in  acids.  Plants, 
however,  are  unable  to  obtain  food  in  such  complex 
forms  of  chemical  combination. 

100.  Action  of  Organic  and  Dilute  Mineral  Acids  upon 
Soils.  —  Dilute  organic  acids,  as  a  I  per  cent  solution 
of  citric  acid,  have  been  proposed  as  solvents  for  the 
determination  of  easily  available  plant  food.  It  has 
been  shown  in  the  case  of  the  Rothamsted  soils  which 
have  produced  50  crops  of  grain  without  manure,  and 
which  are  markedly  deficient  in  available  phosphoric 


FIG.  24.     Wheat  Plant  grown  in  soil  extracted  with  dilute  citric  acid ;  showing 
that  this  solvent  does  not  remove  all  of  the  available  plant  food  from  a  soil. 


THE    CHEMICAL    COMPOSITION    OF    SOILS  85 

acid,  that  a  I  per  cent  solution  of  citric  acid  dissolved 
only  0.003  per  cent  of  phosphoric  acid  while  the  soil 
contained  a  total  of  0.12  per  cent.  In  the  case  of  an 
adjoining  plot  which  had  received  phosphate  manures 
until  the  soil  contained  a  sufficient  amount  of  available 
phosphoric  acid  to  produce  good  crops,  there  was  pres- 
ent 0.03  per  cent  of  phosphoric  acid  soluble  in  a  I  per 
cent  citric  acid  solution.23 

Dilute  organic  acids  are,  to  a  certain  extent,  capable 
of  showing  deficiency  of  plant  food.  A  soil  which 
has  0.03  per  cent  of  potash  or  phosphoric  acid  sol- 
uble in  i  per  cent  citric  acid  is,  as  a  rule,  well  stocked 
with  these  elements  in  available  forms.  Prairie  soils 
of  high  fertility  yield  from  0.03  to  0.05  per  cent  of 
both  potash  and  phosphoric  acid  soluble  in  dilute  or- 
ganic acids ;  soils  which  are  deficient  in  these  elements 
usually  contain  less  than  o.oi  per  cent. 

The  action  of  a  single  organic  acid  of  specific 
strength  cannot  be  taken  as  the  measure  of  fertility 
for  all  soils  and  crops  alike,  because  different  plants 
do  not  have  the  same  amount  or  kind  of  organic  acid 
in  the  sap.  Of  the  various  organic  acids,  citric  pos- 
sesses the  greatest  solvent  action  upon  lime,  magnesia, 
and  phosphoric  acid,  while  oxalic  has  the  strongest 
solvent  action  upon  the  silicates.  Tartaric  acid  ap- 
pears to  be  less  active  as  a  solvent  than  either  citric 
or  oxalic  acid.  The  combined  use  of  dilute  organic 
acids,  as  citric  with  hydrochloric  (sp.  gr.  1.115),  will 
generally  give  an  accurate  idea  of  the  character  of  a 


86  SOILS   AND    FERTILIZERS 

soil.  A  fifth-normal  solution  of  hydrochloric,  or  of 
nitric  acid,  has  also  been  proposed  ^  for  determining 
the  available  plant  food  of  soils ;  a  soil  that  yields 
less  than  25  parts  of  phosphoric  acid  per  million  of 
soil,  as  soluble  in  fifth-normal  nitric  acid,  is  deficient  in 
available  phosphates. 

The  use  of  dilute  organic  acids  renders  it  possible 
to  detect  small  amounts  of  readily  soluble  phosphoric 
acid  and  potash.  It  has  been  stated  that  when  a  soil 
has  been  manured  a  few  years  with  a  phosphate  fer- 
tilizer and  brought  into  good  condition  as  to  available 
phosphoric  acid,  a  chemical  analysis  will  fail  to  detect 
any  difference  in  the  soil  before  and  after  the  treat- 
ment with  fertilizer.  In  the  case  of  hydrochloric  acid 
as  a  solvent,  this  is  true,  as  an  acre  of  soil  to  the  depth 
of  one  foot  weighs  about  3,500,000  pounds  and  500 
pounds  of  a  phosphate  fertilizer  would  increase  the 
total  amount  of  phosphoric  acid  about  0.0002  per  cent, 
which  is  less  than  can  be  accurately  determined  by 
analysis.  When,  however,  a  dilute  organic  acid  is  used, 
only  the  more  easily  soluble  phosphoric  acid  is  dissolved, 
and  this  readily  allows  fertilized  and  unfertilized  soils  to 
be  distinguished.  By  the  use  of  dilute  organic  and  min- 
eral acids  decided  differences  have  been  shown  between 
fertilized  and  unfertilized  soils. 

101.  Sampling  Soils. — A  composite  sample  of  the 
soil  of  a  field  is  obtained  by  taking  several  small  samples 
to  a  depth  of  6  to  12  inches,  from  different  places,  and 


THE   CHEMICAL    COMPOSITION   OF   SOILS 


uniting  them  to  form  one  sample.  Samples  of  subsoil 
also  are  taken  from  the  same  places.  There  is  usually 
a  sharp  line  of  demarca- 
tion between  the  surface 
soil  and  subsoil.  It  is  the 
aim  to  secure  in  each  case 
as  representative  a  sample 
as  possible.  All  coarse 
stones  and  roots  are  re- 
moved and  a  record  is  made 
of  the  amount  of  these. 
The  soil  is  air-dried,  the 
hard  lumps  are  crushed, 
and  the  material  mixed  and 
passed  through  a  sieve  with 
holes  0.5  mm.  in  diameter. 
Only  the  fine  earth  is  used 
for  the  chemical  analysis. 

102.  Analysis  of  Acid- 
soluble  Extract  of  Soils.  — 
Ten  grams  of  soil  are 
weighed  into  a  soil  diges- 
tion flask,  and  locc.  hydro-  FIG. 
chloric  acid  (sp.  gr.  1.115) 
are  added  for  every  gram  of  soil  used.  The  soil  digestion 
flask  is  then  placed  in  a  hot-water  bath  and  the  digestion 
carried  on  for  twelve  to  thirty-six  hours  at  the  temperature 
of  boiling  water.25  After  digestion  is  completed  the 


Soil  Flask  and  Acid  Diges- 
tion of  Soils. 


88  SOILS   AND   FERTILIZERS 

contents  of  the  flask  are  transferred  to  a  filter  and  sepa- 
rated into  the  insoluble  part,  and  the  acid  solution  which 
contains  the  soluble  compounds  of  the  various  elements. 
The  table  on  page  89  gives  a  general  idea  of  the 
process  of  soil  analysis.  One  half  of  the  acid  solution 
is  used  for  obtaining  the  metals  as  noted  on  page  89. 
The  second  half  is  divided  into  two  portions,  —  the 
first  portion  to  be  used  for  the  determination  of  phos- 
phoric acid,  which  is  precipitated  with  ammonium 
molybdate,  and  the  second  portion  to  be  used  for  the 
determination  of  sulphuric  acid,  which  is  precipitated 
as  barium  sulphate.  The  carbon  dioxide  is  determined 
in  a  fresh  portion  of  the  original  soil,  the  acid  being 
liberated  with  hydrochloric  acid  and  the  carbon  dioxide 
retained  by  absorbents  and  weighed.  The  nitrogen 
and  humus  are  determined  in  separate  portions  of  the 
original  soil.  The  analysis  of  soils  involves  the  use  of 
accurate  and  well-known  methods  of  analytical  chem- 
istry, a  discussion  of  which  would  not  be  germane  to 
this  work. 

103.  Value  of  Soil  Analysis.  —  Opinions  differ  as  to 
the  value  of  soil  analysis.  It  is  claimed  by  some  that 
a  chemical  analysis  of  a  soil  is  of  no  practical  value 
because  it  fails  to  give  the  amount  of  available  plant 
food.  A  soil  may  have,  for  example,  0.4  per  cent  of 
potash  soluble  in  hydrochloric  acid  and  still  not  con- 
tain sufficient  available  potash  to  produce  a  good  crop, 
while  another  soil  may  contain  0.2  per  cent  of  potash 


THE   CHEMICAL    COMPOSITION   OF   SOILS 


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9O  SOILS   AND    FERTILIZERS 

soluble  in  hydrochloric  acid  and  produce  good  crops. 
While  these  conditions  are  frequently  observed,  it  does 
not  necessarily  follow  that  the  chemical  analysis  of  a 
soil  is  of  no  value,  as  often  the  results  are  not  correctly 
interpreted.  Then,  too,  other  solvents  than  hydro- 
chloric acid  are  used  for  determining  the  more  active 
forms  of  plant  food.  Hydrochloric  acid  is  generally 
used  because  it  represents  the  limit  of  the  solvent  power 
of  plants.9  The  figures  obtained  by  the  hydrochloric 
acid  solvent  are  valuable,  as  they  indicate  whenever  an 
element  is  present  in  amounts  too  limited  for  crop  pro- 
duction. Suppose  a  soil  contain  0.02  per  cent  of  acid- 
soluble  potash  ;  this  would  be  too  small  an  amount  to 
produce  good  crops.  On  the  other  hand,  the  soil  might 
contain  0.5  per  cent  and  yet  not  have  sufficient  avail- 
able potash  for  crop  growth.  Hence  it  is  that  in 
interpreting  results,  the  hydrochloric  acid  solvent  may 
show  when  a  soil  is  wholly  [deficient  in  any  one  ele- 
ment, as  sometimes  occurs,  but  it  does  not  necessarily 
show  a  deficiency  in  the  case  of  a  soil  rich  in  acid- 
soluble  potash ;  this  can,  however,  be  approximately 
indicated,  by  the  use  of  other  solvents,  as  explained 
in  previous  sections.  Hydrochloric  acid  is  mainly  val- 
uable in  determining  the  general  character  of  the  soil, 
rather  than  its  amount  of  available  plant  food. 

104.  Interpretation  of  Soil  Analysis.  —  In  the  analysis 
of  soils  their  reaction  as  acid,  alkaline,  or  neutral,  should 
be  determined,  because  plant  food  exists  in  a  different 


THE   CHEMICAL    COMPOSITION    OF   SOILS  QI 

form  in  each  class  of  soils.  If  a  soil  contain  from  0.3 
to  0.5  per  cent  or  more  of  lime  and  from  o.i  to  0.4  per 
cent  of  combined  carbon  dioxide,  and  is  not  strongly 
alkaline,  there  is  a  reasonable  content  of  lime  car- 
bonate. If,  however,  the  soil  contain  only  a  trace  of 
carbon  dioxide,  the  lime  is  not  present  as  carbonate,  but 
probably  as  a  silicate,  in  which  case  the  soil  may  be 
deficient  in  active  lime  compounds. 

In  the  case  of  phosphoric  acid,  a  soil  which  gives  an 
alkaline  or  neutral  reaction,  contains  0.15  per  cent  of 
phosphorus  pentoxide  and  is  well  supplied  with  organic 
matter  and  lime,  is  amply  provided  with  phosphoric  acid, 
and  under  such  conditions  the  use  of  phosphate  ferti- 
lizers is  not  required,  except  possibly  for  special  crops. 
Hilgard  states  that  should  the  per  cent  of  phosphoric 
acid  be  as  low  as  0.05,  there  is,  in  all  probability,  a 
deficiency  of  this  element.  It  frequently  happens  that 
in  acid  soils  the  phosphoric  acid  is  unavailable  until  a 
lime  fertilizer  is  used  to  neutralize  the  acid. 

Soils  containing  less  than  0.07  per  cent  of  total 
nitrogen  are  usually  deficient,  and  one  containing  as 
high  as  0.15  or  0.2  per  cent  may  fail  to  respond  to 
crop  production,  but  such  a  case  is  generally  due  to 
some  abnormal  condition  of  the  soil,  as  lack  of  alkaline 
compounds  which  are  necessary  for  nitrification.  The 
appearance  of  the  crop  is  one  of  the  best  indications  as 
to  deficiency  of  nitrogen. 

A  soil  which  contains  less  than  o.io  per  cent  of 
potash  soluble  in  hydrochloric  acid  is  quite  apt  to  be 


92  SOILS   AND    FERTILIZERS 

deficient  in  this  element.  Soils  which  contain  0.5  per 
cent  or  more  of  lime  carbonate  will  produce  good  crops 
on  a  smaller  working  supply  of  potash  than  soils  which 
are  deficient  in  lime.  As  a  rule  the  best  agricultural 
soils  contain  from  0.3  to  0.6  per  cent  of  potash.  Sandy 
soils  of  good  depth  may  contain  less  plant  food  than  the 
figures  given,  and  not  be  in  need  of  fertilizers. 

The  best  results  are  obtained  from  soil  analysis  when 
an  extended  study  is  made  of  the  soils  of  a  locality. 
Then  a  soil  of  that  region  which  fails  to  produce  good 
crops  can  be  compared  with  a  productive  soil  of  known 
composition.  An  isolated  soil  analysis,  like  an  isolated 
analysis  of  well  water,  frequently  fails  in  its  object 
because  of  a  lack  of  proper  normal  standards  for  com- 
parison. Where  extended  series  of  soil  analyses  have 
been  made,  much  valuable  information  has  been  obtained. 

The  term  '  volatile  matter '  of  a  soil  is  sometimes  incor- 
rectly used  for  organic  matter.  The  volatile  matter  in- 
cludes the  organic  matter  and  also  the  water  which  is  held 
in  chemical  combination,  as  in  the  hydrated  silicates. 
A  soil  may  have  a  high  per  cent  of  volatile  matter  and 
contain  very  little  organic  matter.  Indeed,  all  clays 
contain  from  5  to  9  per  cent  of  water  of  hydration. 
The  per  cent  of  humus,  as  will  be  explained  in  the  next 
chapter,  does  not  represent  all  of  the  organic  matter. 

105.  Total  and  Available  Plant  Food.  —  Suppose  a 
soil  contain  0.40  per  cent  of  acid-soluble  potash  and 
field  experiments  indicate  there  is  a  deficiency  of 


THE   CHEMICAL    COMPOSITION   OF   SOILS  93 

available  potash.  This  may  be  due  to  some  abnormal 
condition  of  the  soil,  as  an  insufficient  amount  of  other 
alkaline  compounds,  as  calcium  carbonate,  to  take  the 
place  of  the  potash  which  has  been  withdrawn  by  the 
crop,  or  lost  by  leaching,  in  which  case  the  deficiency  of 
available  potash  can  be  remedied  without  purchasing 
soluble  potash  fertilizer.  Where  a  soil  contains  only 
0.04  per  cent  of  acid-soluble  potash,  the  purchasing  of 
potash  fertilizers  is  more  necessary,  but  with  0.40  per 
cent  the  way  is  open  to  render  this  available  for  crops. 
The  various  ways  of  rendering  acid-insoluble  potash  and 
other  compounds  available  for  crop  production,  as  by 
rotation  of  crops,  use  of  farm  manures,  use  of  lime  and 
green  manures,  or  by  different  methods  of  cultivation 
have  not  been  sufficiently  studied  as  yet  to  offer  a  solu- 
tion to  all  of  the  problems  of  rendering  inert  plant  food 
available. 

106.  Distribution  of  Plant  Food.  —  In  studying  the 
chemical  composition  of  a  soil,  the  surface  soil  and  sub- 
soil both  require  consideration.  It  frequently  happens 
that  these  have  entirely  different  chemical,  as  well  as 
physical,  properties,  and  that  a  soil  fault,  as  lack  of 
potash  in  the  surface  soil,  is  corrected  by  a  high  per 
cent  of  that  element  in  the  subsoil.  This  is  particularly 
true  of  some  of  the  prairie  soils,  where  the  surface  soils 
generally  contain  less  potash  and  lime,  but  more  nitrogen 
and  phosphoric  acid,  than  the  subsoils.  When  jointly 
considered  the  surface  and  subsoil  have  a  good  supply 


94  SOILS    AND    FERTILIZERS 

of  available  plant  food,  but  if  considered  separately  each 
would  have  weak  points. 

Since  plant  food  is  obtained  mainly  from  the  silt  and 
clay,  the  amount  present  in  these  grades  of  particles 
determines  largely  the  reserve  fertility  of  a  soil.  A 
soil  in  which  70  per  cent  of  the  total  potash  is  present 
in  the  silt  and  clay  is  in  better  condition  for  crop  pro- 
duction than  a  similar  soil  with  a  like  amount  of  potash 
which  is  present  mainly  in  the  sand.  Because  a  soil 
has  a  given  composition,  it  does  not  follow  that  all  of 
the  different  grades  of  particles  have  the  same  composi- 
tion. In  fact,  the  different  grades  of  soil  particles  in 
one  soil  may  have  as  varied  a  composition  as  is  met 
with  among  different  soils.26 

The  figures  under  I  in  the  table  give  the  composition 
of  the  particles,  while  under  2.  are  the  results  calculated 
on  the  basis  of  the  total  amount  of  each  element  in  the 
soil.  For  example,  the  clay  contains  1.47  per  cent  of 
potash,  while  50.8  per  cent  of  the  total  potash  of  the 
soil  is  in  the  clay  particles. 

A  soil  may  contain  a  low  per  cent  of  an  element, 
mainly  in  the  finer  particles  and  evenly  distributed  so 
the  crop  is  better  supplied  with  food  than  if  more  were 
present  in  the  larger  particles,  unevenly  distributed. 
The  distribution  of  plant  food  in  the  soil  has  not  been 
so  extensively  studied  as  the  question  of  total  plant 
food.  The  distribution  of  plant  food  in  both  surface 
soil  and  subsoil,  as  well  as  in  the  various  grades  of 
soil  particles,  is  an  important  factor  of  fertility. 


THE    CHEMICAL    COMPOSITION    OF    SOILS 


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96  SOILS   AND    FERTILIZERS 

107.  Composition  of  Typical  Soils.  —  A  few  examples 
are  given,  in  tabular  form,  of  the  chemical  composition 
of  soils  from  different  regions  in  the  United  States.    On 
account  of  variations  in  the  same  locality,  the  figures 
represent  the  composition  of   only  limited   soil  areas. 
There  have  been  made  in  the  United  States  a  large 
number  of  soil  analyses  which  as  yet  have  not  been 
compiled  or  studied  in  a  systematic  way. 

108.  Alkaline  Soils.  —  When  a  soil  contains  enough 
alkaline  salts,  as  sodium  sulphate,  sodium  or  potassium 
carbonate  or  chloride,  to  be  destructive  to  vegetation, 
it  is  called  an  'alkali'  soil.     These  soils  are  found  in 
semi-arid  regions,  and  wherever  conditions  have  been 
such  that  the  alkaline  compounds  have  not  been  drained 
from   the   soil.     Occasionally   calcium   chloride   is   the 
destructive  material.    Sodium  sulphate  is  a  milder  form. 
Alkaline  carbonates  are  destructive  to  vegetation  when 
present  to  the  extent  of  more  than  i  part  per  1000  parts 
of   soil.     When  evaporation  takes  place,  the  alkaline 
compounds  are  deposited  as  a  coating  on  the  surface 
of  the  soil.     Of  these  sodium  carbonate  is  one  of  the 
most   injurious ;   it  exerts    a   solvent   action   upon   the 
humus,  forming  a  black  solution  which  evaporates  and 
leaves  the  so-called  'black   alkali.'      Many  soils  sup- 
posed to  be  strongly  alkaline,  because  a  white  coating 
is  formed  on  the  surface,  simply  contain  so  much  lime 
carbonate  that  a  deposit  is  formed.    Excellent  soils  have 
been  passed  over  as  '  alkali '  soils  when  in  reality  they 
are  limestone  soils. 


THE    CHEMICAL    COMPOSITION    OF    SOILS 


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99 

109.  Improving  Alkali  Soils.27  —  When  a  large  tract  of 
alkali  is  to  be  brought  under  cultivation,  the  amount  and 
kind  of  prevailing  alkaline  compound  should  be  deter- 
mined by  chemical  analysis.  It  frequently  happens  that 
improved  drainage,  coupled  with  a  judicious  irrigation 
system,  is  all  the  treatment  necessary.  If  the  prevail- 
ing alkali  is  sodium  carbonate,  a  dressing  of  land  plaster 
may  be  applied  so  as  to  change  the  alkali  from  sodium 
carbonate  to  sodium  sulphate,  a  less  destructive  form, 
the  reaction  being 

Na2CO3  +  CaSO4=  CaCO3  +  Na2SO4. 

Some  shrubs,  as  greasewood,  and  weeds,  as  Russian 
thistle,  take  from  the  soil  large  amounts  of  alkaline 
matter,  and  it  is  sometimes  advisable  to  remove  a  num- 
ber of  such  crops  so  as  to  reduce  the  alkali.  A  slightly 
beneficial  effect  is  occasionally  noticed  on  small  '  alkali ' 
spots  where  straw  has  been  burned  and  the  ashes  used, 
forming  potassium  silicate.  As  a  rule,  however,  ashes 
are 'more  injurious  than  beneficial  on  an  'alkali'  soil. 
Irrigation  and  thorough  drainage,  if  continued  long 
enough,  will  effect  a  permanent  cure.  Irrigation  with- 
out drainage  causes  a  worse  alkaline  condition  by  bring- 
ing to  the  surface  subsoil  alkali.  All  irrigated  lands 
should  be  provided  with  suitable  drainage  systems  to 
prevent  accumulation  of  alkaline  salts.  The  waters 
from  some  streams  and  wells  are  unsuited  for  irrigation 
because  they  contain  too  much  alkaline  matter. 

Mildly  alkaline  soils  will  usually  repay  in  crop  pro- 


IOO  SOIL90AND    FERTILIZERS 

duction  all  the  labor  which  is  expended  upon  them,  and 
when  brought  under  cultivation  are  frequently  very 
fertile.  Some  alkaline  material  in  a  soil  is  beneficial ; 
in  fact,  many  soils  would  be  more  productive  if  they 
contained  a  small  amount.  It  is  the  excess  of  alkali 
that  is  destructive  to  plant  life. 

When  the  places  are  small  and  located  so  they  can 
be  underdrained  at  comparatively  little  expense,  this 
should  be  done,  as  it  will  prove  the  best  and  most  per- 
manent way  of  removing  the  alkali.  Good  surface 
drainage  should  also  be  provided.  Quite  frequently  a 
quarter  or  more  of  the  total  alkali  in  the  soil  will,  in  a 
dry  time,  be  found  near  and  on  the  surface.  In  such 
cases,  and  if  the  spots  are  small,  a  large  amount  of  the 
alkali  can  be  removed  by  scraping  the  surface  and  then 
carting  the  scrapings  away  and  dumping  them  where 
they  can  do  no  damage. 

When  preparing  a  mildly  alkaline  spot  for  a  crop, 
deep  plowing  should  be  practiced,  so  as  to  open  up 
the  soil  and  remove  the  excess  of  alkali  from  the  sur- 
face. Where  manure,  particularly  horse  manure,  can  be 
obtained,  these  spots  should  be  manured  very  heavily. 
The  horse  manure,  when  it  decomposes,  furnishes  acid 
products,  which  combine  with  the  alkaline  salts.  The 
manure  also  prevents  rapid  surface  evaporation.  Oats 
are  about  the  safest  grain  crop  to  seed  on  an  alkali  spot 
because  the  oat  plant  is  capable  of  thriving  in  an  alka- 
line soil  where  many  other  grain  crops  fail. 

Alkali  soils  are  usually  deficient  in  available  nitro- 


THE   CHEMICAL   COMPOSITION   OF   SOILS  IOI 

gen.  The  organism  which  carries  on  the  work  of 
changing  the  humus  nitrogen  to  available  forms  cannot 
thrive  in  a  strong  Ulkaline  solution.  In  many  of  these 
soils,  as  demonstrated  in  the  laboratory,  nitrification 
cannot  take  place.  After  thorough  drainage  and  prepa- 
ration for  a  crop,  a  few  loads  of  good  soil  from  a  fertile 
field  sprinkled  on  alkali  spots  will  do  much  to  encourage 
nitrification,  by  introducing  the  nitrifying  organisms. 

For  a  more  extended  account  of  the  cause  of  alkali 
soils,  and  methods  for  improving  them,  the  student  is 
referred  to  Hilgard's  "Soils." 

110.  Acid  Soils.  —  When  a  soil  is  deficient  in  active 
alkali,  and  there  is  an  excess  of  organic  material,  humic 
acid  is  formed  from  the  decay  of  the  animal  and  vege- 
table matter.  Acid  soils  are  readily  detected  by  the 
reaction  which  they  give  with  sensitive  litmus  paper. 
In  making  the  test  the  moistened  soil  is  pressed  against 
blue  litmus  paper,  which  changes  to  red  in  the  presence 
of  free  acids.  Acid  soils  are  made  productive  by  using 
lime  and  other  alkaline  material  to  neutralize  the  humic 
acid  before  applying  farm  and  other  manures.  Acid  soils 
are  not  suitable  for  the  production  of  clover  and  legumes. 

Experiments  by  Wheeler  at  the  Rhode  Island  Ex- 
periment Station  indicate  that  there  are  large  areas 
of  acid  soils  in  the  eastern  states  which  are  much 
improved  when  treated  with  air-slaked  lime.30  There 
is  great  difference  in  the  power  of  plants  to  live  in 
acid  soils.  Some  agricultural  crops  as  legumes  are  par- 


IO2  SOILS   AND    FERTILIZERS 

ticularly  sensitive,  while  many  weeds  have  such  strong 
power  of  endurance  that  they  thrive  in  the  presence  of 
acids.  Weeds  frequently  reflect  the  character  of  a  soil 
as  to  acidity,  in  the  same  way  that  an  alkali  soil  is 
indicated  by  the  plants  produced.  The  acid  and  alka- 
line compounds  of  the  soil  greatly  influence  the  bacterial 
flora.  In  the  presence  of  strong  acids  or  alkalis,  many 
of  the  bacterial  changes  necessary  for  the  elaboration  of 
plant  food  fail  to  take  place. 

THE  ORGANIC  COMPOUNDS  OF  SOILS 

111.  Sources  of  the  Organic  Compounds  of  Soils.  — 
The  organic  compounds  of  soils  are  composed  of  the 
elements  carbon,  hydrogen,  oxygen,  and  nitrogen. 
When  vegetable  and  animal  material  undergoes  decay 
in  contact  with  the  soil,  compounds,  as  carbon  dioxide, 
water,  ammonia,28  organic  acids,  and  various  derivatives 
are  formed,  while  some  of  the  organic  acids  unite  with 
the  minerals  of  the  soil  to  form  humates.  Micro- 
organisms take  an  important  part  in  the  decay  of  ani- 
mal and  vegetable  matter  and  the  production  of  organic 
compounds.  In  some  soils,  the  organic  compounds  of 
plants,  as  cellulose,  proteids,  and  carbohydrates,  are 
present,  while  in  others  they  have  undergone  partial 
oxidation.  Some  authorities  claim  that  a  portion  of  the 
initial  organic  matter  of  soils  is  the  result  of  the  work- 
ings of  carbon  assimilating  micro-organisms.  The  main 
source  of  the  soil's  organic  compounds,  however,  is  the 


THE    CHEMICAL    COMPOSITION    OF    SOILS  IO3 

accumulated  animal  and  vegetable  remains  in  various 
stages  of  decay.  The  organic  matter  of  soils  is  a 
mechanical  mixture  of  a  large  number  of  organic  com- 
pounds, many  of  which  have  not  yet  been  studied. 

112.  Classification  of  the  Organic  Compounds.  —  Vari- 
ous attempts  have   been  made  to  classify  the  organic 
compounds    of    the    soil.       An    old    classification    by 
Miilder29  was   humic,  ulmic,   crenic,    and   approcrenic 
acids.     None  of  these  contain   more  than  4  per  cent 
nitrogen,  while  organic  matter  with   8  to  10  per  cent 
and  in  some   cases    18    per   cent    is  quite  frequently 
met  with;  hence  this  classification  is  incomplete  as  it 
includes  only  a  part  of  the  organic  compounds  of  the 
soil.     For  practical  purposes  the  organic  compounds  of 
soils  may  be  divided  into  three  classes:  (i)  those  of  low 
nitrogen  content,  I  to  4  per  cent  of  nitrogen ;  (2)  those 
of  medium  nitrogen  content,  5  to   10  per  cent;  and  (3) 
those  of  high  nitrogen  content,  1 1  to  20  per  cent. 

113.  Humus.  —  The   term    '  humus '   is   employed  to 
designate  the  most  active  of  the  organic  compounds  ; 
it  is  the  animal  and   vegetable  matter  of  the  soil  in 
intermediate  forms  of  decomposition.     From  different 
soils,  it  is  extremely  varied  in  composition ;  in  one  soil 
it  may  have  been  derived  mainly  from  cellulose,  while 
in  another  from  a  mixture  of  cellulose,  proteid  bodies, 
and  other  organic  compounds.    The  term  'humus,'  unless 
qualified,  is  a  very  indefinite  one.     Humus  is  obtained 


IO4  SOILS    AND    FERTILIZERS 

by  extracting  the  soil  with  a  dilute  alkali,  as  ammonium 
hydroxide,  after  treating  with  a  dilute  acid  to  remove 
the  lime  which  renders  the  humus  insoluble. 

114.  Humification  and  Humates.  —  When  the  animal 
and  vegetable  matter  incorporated  with  soils  undergoes 
decomposition,  there  is  a  union  of  some  of  the  organic 
compounds  with  the  base-forming  elements.  The  decay- 
ing organic  matter  produces  organic  products  of  an  acid 
nature.  The  organic  acids  and  the  base-forming 
products  unite  to  form  humates  or  organic  salts,  which 
are  neutral  bodies.  This  process  is  humification.18 

Humic  acid  +  calcium  carbonate  =  calcium  humate  +  CO2. 
Humic  acid  +  potassium  chloride  =  potassium  humate  and  solu- 
ble chlorides. 

That  a  union  occurs  between  the  organic  matter  and 
the  soil  has  been  demonstrated  by  mixing  with  soils 
known  amounts  of  definite  organic  compounds  and 
various  organic  materials,  as  cow  manure,  green  clover, 
meat  scraps,  and  sawdust,  and  allowing  humification  to 
go  on  for  a  year  or  more.  After  humification  had 
taken  place,  the  humus  extracted  from  the  soil  con- 
tained more  potash  and  phosphoric  acid,  than  were 
present  in  the  humus  of  the  original  soil  and  the  humus- 
forming  material,  showing  a  chemical  change  had  taken 
place  between  the  organic  matter  and  the  soil.  The 
power  of  various  organic  substances  to  produce  humates 
is  illustrated  in  the  following  table :  18>  ^ 


THE    CHEMICAL    COMPOSITION    OF    SOILS 


105 


HUMIC  PHOS- 
PHORIC ACID 

HUMIC 
POTASH 

Grams     . 

Grams 

Cow  manure  humus  : 

1.  17 

1  .06 

In  final  humus  product  (after  humifica- 

T     A-7 

O  AC 

O  21 

Green  clover  humus  : 
In  original  soil  and  clover   

In  final  humus  product    .          .     .     i>rii-u> 

3-21 

5.26 

Gain  in  huniic  forms  «y  '•>( 

3-74 
o  CT. 

O   77 

Meat  scrap  humus  : 
In  original  meat  scraps  and  soil     .     .;  «; 
In  final  humus  product     

1.07 

^•JJ 

(Loss) 
0.25 

I.lo 

0.36 

Oil 

Oil 

Sawdust  humus  : 
In  original  sawdust  and  soil      .... 
In  final  humus  product     

0.85 
r>  78 

0.67 

Oaf  straw  humus  : 
In  original  straw  and  soil          .... 

o 

In  final  humus  product    

2.42 

2.41 

Wheat  gliadin  humus  : 
In  orisrinal  sfliadin  and  soil  .        ?.-•>/ 

o             o 

In  final  humus  product    

1.055 

O.ig 

i.  220 

O.24 

Egg  albumin  humus  : 
In  original  albumin  and  soil      .... 
In  final  humus  product    

I.OI 

O.2O 

(Jain    

O.IO 

O.OJ. 

io6 


SOILS   AND   FERTILIZERS 


115.  Comparative  Value  and  Composition  of  Humates. 
—  The  humus  produced  from  a  nitrogenous  material, 
as  meat  scraps,  is  more  valuable  than  from  cellulose 
bodies,  as  sawdust,  because  the  former  has  greater 
power  of  combining  with  the  phosphoric  acid  and 
potash  of  the  soil.  The  non-nitrogenous  compounds, 
as  cellulose,  starch,  and  sugar,  undergo  fermentation  but 
seem  to  possess  little,  if  any,  power  to  form  humates. 
There  is  also  a  great  difference  in  soils  as  to  their 
humus-producing  power.  Soils  deficient  in  lime  or  al- 
kaline compounds  possess  only  a  feeble  power  to  pro- 
duce humates.  There  is  too  a  marked  variation  in 
the  composition  of  the  humus  from  different  kinds  of 
organic  matter.  Straw,  sawdust,  and  sugar,  materials 
rich  in  cellulose  and  other  carbohydrates,  yield  a  humus 
characteristically  rich  in  carbon  and  poor  in  nitrogen. 
Materials  rich  in  nitrogen,  like  meat  scraps,  green  clover, 
and  manure,  produce  a  more  valuable  humus,  rich  in 
nitrogen  and  possessing  the  power  to  combine  with  the 
potash  and  phosphoric  acid  of  the  soil  to  form  humates. 

COMPOSITION  OF  HUMUS  PRODUCED  BY 


Cow 

Green 

Meat 

Wheat 

Oat 

Saw- 

manure 

clover 

scraps 

flour 

straw 

dust 

Carbon 

41.95 

54-22 

48.77 

5I.O2 

54-3° 

49.28 

57.84 

Hydrogen 

6.26 

3-40 

4-3° 

3-82 

2.48 

3-33 

3-04 

Nitrogen 

6.16 

8.24 

10.96 

5.02 

2.50 

0.32 

0.08 

Oxygen 

45-63 

34-14 

35-97 

40.14 

40.72 

47.07 

39-04 

Total 

100.  CO 

IOO.OO 

IOO.OO 

IOO.OO 

IOO.OO 

IOO.OO 

IOO.OO 

THE   CHEMICAL    COMPOSITION   OF    SOILS 


Highest 

Lowest 

Difference 

Carbon    

17.84 

41  .QC 

1C.  80 

Hydrogen     

6.26 

2.48 

1.78 

Nitrogen       

10.06 

0.08 

10.88 

Oxvsren   . 

47.07 

•tA.  14. 

12.  Q^ 

Variations  in  composition  are  noticeable.  The  hu- 
mus produced  from  each  material,  as  green  clover,  oat 
straw,  or  sawdust,  is  different  from  that  produced  from 
any  other  material.  The  humus  from  green  clover  is 
very  complex  in  nature.  It  contains  both  nitrogenous 
and  non-nitrogenous  compounds,  and  each  class  has  a 
different  action  in  humification  processes;  hence  it  fol- 
lows that  the  green  clover  humus  must  be  a  complex 
mixture  of  both  nitrogenous  and  non-nitrogenous  bodies. 

The  nature  of  the  humus,  whether  nitrogenous  or 
non-nitrogenous,  is  important.  Humus  produced  from 
sawdust  and  humus  from  meat  scraps  may  be  taken  as 
types  of  non-nitrogenous  and  nitrogenous  humus. 

116.  Value  of  Humates  as  Plant  Food. — Various 
opinions  have  been  held  regarding  the  actual  value,  as 
plant  food,  of  this  product  from  partially  decayed  an- 
imal and  vegetable  matter.  Humus  was  formerly  re- 
garded as  composed  only  of  carbon,  hydrogen,  and 
oxygen,  and  inasmuch  as  plants  obtain  these  elements 
from  water  and  from  the  carbon  dioxide  of  the  air,  no 
value  was  assigned  to  it.  Later  investigators  added 


io8 


SOILS   AND   FERTILIZERS 


nitrogen  to  the  list,  but  stated  that  the  nitrogen,  when 
combined  with  the  humus  and  before  undergoing  fer- 
mentation, was  of  no  value  as  plant  food. 

Recent  investigations  have  proved  that  the  mineral 
elements  combined  with  the  organic  matter  of  soils  are 
of  value  as  plant  food,9  and  that  crops  grown  on  the 

black  soils  of  Russia 
obtain  a  large  part  of 
their  mineral  food 
from  organic  combi- 
nations.84 Culture  ex- 
periments show  that 
plants  like  oats  and 
rye  may  obtain  their 
mineral  food  entirely 
from  humate  sources. 
Seeds  when  planted 
in  a  mixture  of  pure 
sand  and  neutral 
humates  from  fertile 
soils,  produced  per- 
fect plants.  In  order 
to  secure  normal  con- 
ditions, a  little  lime 

was  added  to  prevent  the  formation  of  humic  acid,  and 
the  organisms  found  in  fertile  fields  were  introduced. 
The  following  results  are  given  of  oats  which  were 
grown  when  the  only  supply  of  mineral  food  was  in 
humate  forms : 


Total  /nso/ut>/e  Matter- . 


FIG.  26.  Graphic  Composition  of  200  Soils, 
showing  the  Proportional  Amounts  of  the 
Various  Soil  Constituents. 


I.   Nitrogen.    2.  Potash, 
acid. 


3.   Phosphoric 


THE    CHEMICAL    COMPOSITION    OF    SOILS 


IO9 


NITROGEN  AND  ASH  ELEMENTS9 


IN  Six  OAT 

SEEDS 

IN  Six  MATURE 
PLANTS 

Gram 

Gram 

O.OO4O 
OOOI3 
O.OOOI 
O.OOO2 
O.OOO5 

0.0016 

O.OOOI 
O.OO26 

0.0556 
0.0640 
O.OO79 
O.O249 
O.OIIO 
0.0064 
0.0960 
O.OOgO 
0.7300 

Phosphoric  anhydride  

Sulphuric  anhydride     

The  facts  that  plants  feed  on  humate  compounds,  and 
decaying  animal  and  vegetable  matter  produce  humates 
from  the  inert  potash  and  phosphoric  acid  of  the  soil, 
have  an  important  bearing  upon  crop  production  in 
pointing  out  a  way  by  which  inert  plant  food  may  be  con- 
verted into  more  active  and  available  forms.  This 
also  explains  that  stable  manure  is  valuable  partly 
because  it  makes  the  inert  plant  food  of  the  soil  more 
available. 

117.  Mineral  Matter  combined  with  Humus.  —  When 
the  humus  compounds  are  separated  from  a  soil,  they 
contain  appreciable  amounts  of  phosphorus,  potassium, 
and  compounds  of  other  elements  which  are  soluble  in 
the  reagents  used  for  obtaining  the  humus.  If  the 


no 


SOILS   AND    FERTILIZERS 


humus  materials  are  precipitated  and  purified  by  wash- 
ing, the  impurities  are  largely  removed  and  the  mineral 
elements  which  are  chemically  united  with  and  form  a 
part  of  the  humus  can  then  be  determined.  Analyses 
of  eight  samples  of  purified  humus  ash,  from  produc- 
tive prairie  soils,  gave  the  following  average  :  9 


PER  CENT 


Ash  (precipitated  humus) 
Composition  of  ash : 

Silica 

Potash,  K2O     . 

Soda,  Na2O 

Lime,  CaO 

Magnesia,  MgO 

Ferric  oxide,  Fe2O3  . 

Alumina,  A12O3 

Phosphoric  acid,  P2O5 

Sulphuric  acid,  SO3 

Carbonic  acid,  CO2 


12.24 

61.97 
7.20 

8.13 
0.09 
0.36 
3-12 
3-48 
12.37 
0.98 
1.64 


118.   Amount  of  Plant  Food  in  Humate  Forms.  —  In  a 

prairie  soil  containing  3.5  per  cent  of  humus  there  are 
present  100,000  pounds  of  humus  per  acre.  Combined 
with  this  humus  are  from  500  to  1500  pounds  each  of 
phosphoric  acid  and  potash.  Similar  soils  which  have 
been  under  long  cultivation  without  the  restoration  of 
any  humus,  contain  from  300  to  500  pounds  each  of 
humic  potash  and  phosphoric  acid.9  A  decline  in  crop- 
producing  power  has  in  many  cases  been  brought 


THE    CHEMICAL    COMPOSITION    OF    SOILS  III 

about  by  the  loss  of  the  plant  food  combined  with  the 
humus. 

119.  Loss  of  Humus.  —  Loss  of  humus  from  soils  is 
caused  by  oxidation  and  by  fires.  Any  method  of 
cultivation  which  accelerates  oxidation  reduces  the 
humus  content.  In  many  of  the  western  prairie  soils 
which  have  been  under  continuous  grain  cultivation 
for  thirty  years  or  more,  the  amount  of  humus  has  been 
reduced  one  half.  Summer  fallowing  also  causes  a  loss 
of  humus.  When  land  is  continually  under  the  plow, 
and  no  manures  are  used,  the  humus  is  rapidly  oxidized, 
and  there  is  left  in  the  soil  only  the  organic  matter  that 
is  slow  to  decay. 

Forest  and  prairie  fires  have  been  very  destructive 
to  the  organic  compounds  of  the  soil.  A  soil  from 
Hinckley,  Minn.,  before  the  great  forest  fire  of  1893, 
showed  1.69  per  cent  humus  and  0.12  per  cent  nitro- 
gen.17 After  the  fire  there  were  present  0.41  per  cent 
humus  and  0.03  per  cent  nitrogen.  The  forest  fire 
caused  a  loss  of  2500  pounds  of  nitrogen  per  acre.  In 
clearing  new  land,  particularly  forest  land,  there  is 
frequently  an  unnecessary  destruction  of  humus  mate- 
rials. Instead  of  burning  all  of  the  vegetable  matter,  it 
would  be  better  economy  to  leave  some  in  piles  for 
future  use  as  manure.  When  all  of  the  vegetable  mat- 
ter has  been  burned,  two  or  three  good  crops  are 
obtained,  but  the  permanent  crop-producing  power  of 
the  land  is  reduced  because  of  the  loss  of  nitrogen  and 


112 


SOILS    AND    FERTILIZERS 


humus.  When  the  vegetable  matter  has  been  only 
partially  removed,  the  crops  at  first  may  be  smaller, 
but  in  a  few  years  returns  will  be  greater  than  if  all 
of  the  vegetable  matter  had  been  burned. 

120.  Physical  Properties  of  Soils  influenced  by  Humus. 
—  The  physical  properties  of  a  soil  may  be  entirely 
changed  by  the  addition  or  the  loss  of  humus.  The 
influence  of  humus  upon  the  weight,  color,  heat,  and 
water-retaining  power  of  soils  is  discussed  in  the  chap- 
ter on  the  physical  properties  of  soils.  Soils  reduced  in 
humus  content  have  less  power  of  storing  up  water  and 
resisting  drought.  This  fact  is  illustrated  in  the  follow- 
ing table : 31 

PER  CENT  WATER 


IN  SOIL 

AFTER  10  HOURS' 
EXPOSURE  IN 
TRAY,  TO  SUN 

Soil  rich  in  humus  (3.75  per  cent)     .     .     . 
Adjoining  soil  poorer  in  humus  (2.50  per  cent) 

16.48 
12.14 

6.12 

3-94 

121.  Humic  Acid.  —  In  the  absence  of  calcium  car- 
bonate or  other  alkaline  material,  the  vegetable  matter 
of  soils  through  processes  of  decay  may  form  organic 
acids  destructive  to  the  growth  of  some  crops.  The  com- 
position and  physical  properties  of  these  organic  acids 
have  never  been  determined,  and  the  indefinite  term 
'  humic  acid  '  has  been  applied  to  them.  Succinic  acid 


THE    CHEMICAL    COMPOSITION    OF    SOILS 


has  been  reported  present  in  peaty  soils.  Acid  soils 
can  be  distinguished  by  their  action  upon  blue  litmus 
paper,  and  the  acidity  can  be  readily  corrected  by  the  use 
of  lime  or  wood  ashes.  A  soil  may,  however,  give  an 
acid  reaction  and  contain  a  fair  amount  of  lime  as  a 
silicate.  Studies  conducted  by  the  Rhode  Island  Ex- 
periment Station  indicate  that  the  areas  of  acid  soils  are 
quite  extensive. 

122.    Soils  in  Need   of   Humus.  —  Sandy   and    sandy 
loam  soils   that   have 
been  cultivated  for  a 
number    of    years   to 
corn,     potatoes,     and 
small    grains    without 
rotation  of  crops  or  the 
use  of  stable  manures 
are  deficient  in  humus.     Clay  soils,  as  a  rule,  are  not  in 
need  of  humus  so  much  as  loam  and  sandy  soils.     The 

mechanical  condition  of 
heavy  clay  is,  however,  im- 
proved by  the  addition  of 
humus-forming  material. 
The  addition  of  humus  to 
loam  and  sandy  soils  is 
beneficial  in  preventing 
drifting,  because  it  binds  together  the  soil  particles. 
There  are  but  few  arable  soils,  under  ordinary  cultiva- 
tion, to  which  it  is  not  safe  to  add  humus-forming  mate- 


FIG.  27.     Humus  from  Old  Soil. 


FIG.  28.    Humus  from  New  Soil. 


SOILS   AND    FERTILIZERS 


rials  either  alone  or  jointly  with  lime.  Ordinary  prairie 
soils,  for  the  first  ten  years  after  breaking,  are  usually 
well  supplied.  Swampy,  peaty,  and  muck  soils  contain 
large  amounts  ;  in  fact,  they  are  often  overstocked  and 
are  improved  by  reducing  the  humus  content.  'Alkali' 
soils  are  usually  deficient  in  humus. 

123.  Active  and  Inactive  Humus. — When  soil  has 
been  long  under  cultivation,  and  no  manures  have  been 
used,  the  nitrogen  and  mineral  matters  combined  with 
the  humus  are  reduced.  The  humus  from  long-culti- 
vated fields  contains  a  higher  per  cent  of  carbon  than 
from  well-manured  or  new  land;  it  is  also  less  active 
because  of  the  carbon  which  does  not  readily  undergo 
oxidation.9 


HUMUS  FROM 
NEW  SOIL 

HUMUS  FROM 
OLD  SOIL 

Per  cent 

Per  cent 

44.12 

6.00 
35-i6 

8.12 

6.60 

50.10 
4.80 
3370 
6.50 
4.90 

Nitrogen     

Ash    

Tot&l  humus  nicitcriul      

5-3° 

3-38 

124.  Influence  of  Different  Methods  of  Farming  upon 
Humus.  —  The  system  of  farming  has  a  direct  effect 
upon  the  humus  content  and  the  composition  of  the 


THE    CHEMICAL    COMPOSITION    OF    SOILS 


soil.  Where  the  crops  are  systematically  rotated,  live 
stock  is  kept,  and  the  manure  judiciously  used,  the 
crop-producing  power  of  the  land  is  not  lowered,  as  in 
the  case  of  the  one-crop  system.  The  influence  of  dif- 
ferent systems  of  farming  upon  the  humus  content  and 
other  properties  of  the  soil  may  be  observed  in  the  fol- 
lowing table : 31 


CHARACTER  OF  SOIL 

'eight  per  cu.  ft. 

II  11  II  U 

umus 
cr  cent 

Sc 

bo  v 
o  o 

•c  c  «  g 

!"!  s  g 

'ater-holding 
ipacity 
:r  cent 

£6 

fcd, 

&,  u-cd, 

'>  od, 

I.  Cultivated  thirty-five   years; 

rotation   of  crops  and  ma- 

nure ;    high    state    of   pro- 
ductiveness   

70 

T..T.2 

O.O4. 

48 

2.    Originally  same  as  i  ;    con- 

/ 

O  J 

V*M^ 

*TW 

tinuous   grain  cropping  for 

thirty-five  years  ;   low  state 

of  productiveness      .     .    . 

72 

1.  80 

0.16 

0.01 

39 

3.   Cultivated    forty-two    years  ; 

systematic      rotation      and 

manure  ;  good  state  of  pro- 
ductiveness       

7.4.6 

0.26 

4.   Originally  same  as  3  ;   culti- 

O 'rj 

vated  thirty-five   years  ;    no 

systematic  rotation  or  ma- 

nure ;  medium  state  of  pro- 
ductiveness   

67 

O.2I 

0.0-1 

C7 

w/ 

' 

-'•^J 

01 

CHAPTER   IV 

NITROGEN   OF    THE    SOIL   AND    AIR,    NITRIFICATION. 
AND   NITROGENOUS   MANURES 

125.   Importance   of  Nitrogen   as   Plant  Food.  —  The 

illustration  (Fig.  29)  shows  an  oat  plant  which  received 
no  nitrogen,  while  compounds  containing  potassium, 
phosphorus,  calcium,  and  other  essential  elements  of 
plant  food  were  liberally  supplied.  Observe  the  pecul- 
iar and  restricted  growth  and  the  limited  root  develop- 
ment. The  leaves  were  yellowish,  showing  lack  of 
nitrogen  for  chlorophyll  formation. 

In  the  absence  of  nitrogen  a  plant  makes  no  ap- 
preciable growth.  With  only  a  limited  supply,  growth 
is  begun  in  a  normal  way ;  but  as  soon  as  the  available 
nitrogen  is  used  up,  the  lower  and  smaller  leaves  begin 
gradually  to  die  down  from  the  tips,  and  all  of  the 
plant's  energy  is  centered  in  one  or  two  leaves.  In  one 
experiment  when  only  a  small  amount  of  nitrogen  was 
supplied,  the  plant  struggled  along  in  this  way  for 
about  nine  weeks,  making  a  total  growth  of  but  six 
and  one  half  inches.9  Just  at  the  critical  point  when 
the  plant  was  dying  of  nitrogen  starvation,  a  few  mil- 
ligrams of  calcium  nitrate  were  given.  In  thirty-six 
hours  the  plant  showed  signs  of  renewed  life,  the  leaves 

116 


NITROGEN,    NITRIFICATION,    NITROGENOUS    MANURES      1 1/ 


assumed  a  deeper  green,  new  growth  was  begun,  and 
finally  four  seeds  were  produced. 
During  the  time  of  seed  formation 
more  nitrogen  was  added,  but  with  no 
beneficial  result.  All  of  the  essential 
elements  for  plant  growth  were  liber- 
ally provided,  except  nitrogen,  which 
was  very  sparingly  supplied,  until  near 
the  period  of  seed  formation. 

When  plants  have  reached  a  certain 
period  in  their  development,  and  have 
been  starved  for  want  of  nitrogen,  the 
later  application  of  this  element  does 
not  produce  normal  growth,  as  the  en- 
ergy of  the  plant  appears  to  have  been 
used  up  in  searching  for  food.  Nitro- 
gen, as  well  as  potash,  lime,  and  phos- 
phoric acid,  are  all  necessary  while 
plants  are  in  the  first  stages  of  growth. 

In  the  case  of  wheat,  nitrogen  is  as- 
similated more  rapidly  than  are  any 
of  the  mineral  elements.  Before  the 
plant  heads  out,  over  85  per  cent  of 
the  total  nitrogen  required  has  been 
taken  from  the  soil.37  Corn  also  absorbs 
all  of  its  nitrogen  from  four  to  five 
weeks  before  the  crop  matures.  Flax 
takes  up  75  per  cent  during  the  first  fifty  days  of 
growth.38 


FIG.  29.  Oat  Plant 
grown  without  Ni- 
trogen. 


Il8  SOILS   AND   FERTILIZERS 

Nitrogen  is  demanded  by  all  crops ;  it  forms  the  chief 
building  material  for  the  proteids  of  plants.  In  the  ab- 
sence of  sufficient  nitrogen,  the  rich  green  color  is  not 
developed;  the  foliage  is  of  a  yellowish  tinge.  Nitro- 
gen is  one  of  the  constituents  of  chlorophyll,  the  green 
coloring  matter  of  plants ;  hence  when  there  is  a  lack  of 
nitrogen  only  a  limited  amount  of  chlorophyll  can  be 
produced.  Plants  with  large,  well-developed  leaves  of 
a  rich  green  color  are  not  suffering  for  this  element. 
Nitrogenous  fertilizers  have  a  tendency  to  produce  a 
luxurious  growth  of  foliage,  deep  green  in  color. 


ATMOSPHERIC    NITROGEN    AS    A    SOURCE    OF    PLANT 

FOOD 

126.  Early  Views.  —  In  addition  to  carbon,  hydrogen, 
and  oxygen,  which  form  the  organic  compounds  of 
plants,  it  was  known  as  early  as  the  beginning  of  the 
present  century  that  plants  also  contain  nitrogen.  The 
sources  of  carbon,  hydrogen,  and  oxygen  for  crop  pur- 
poses were  much  easier  to  determine  and  understand 
than  the  sources  of  nitrogen.  Priestley,  the  discoverer 
of  oxygen,  believed  that  the  free  nitrogen  of  the  air 
was  a  factor  in  supplying  plant  food.  De  Saussure  ar- 
rived at  just  the  opposite  conclusion.  Neither  of  these 
assumptions  was  convincing  because  methods  of  chem- 
ical analysis  had  not  yet  been  sufficiently  perfected  to 
solve  the  question.39 


NITROGEN,    NITRIFICATION,    NITROGENOUS   MANURES 


127.  Boussingault's  Experiments.  —  Boussingault  was 
the  first  to  make  a  careful  study  of  the  subject.  In  a 
prepared  soil,  free  from  nitrogen,  and  containing  all  of 
the  other  elements  necessary  for  plant  growth,  he  grew 
clover,  wheat,  and  peas,  carefully  determining  the 
nitrogen  in  the  seed.  The  plants  were  allowed  free 
access  to  the  air,  being  simply  protected  from  dust,  and 
were  watered  with  distilled  water.  But  little  growth 
was  made.  At  the  end  of  two  months  the  plants  were 
submitted  to  chemical  analysis,  and  the  amount  of  ni- 
trogen present  was  determined. 

The  results  are  given  in  the  following  table  :*° 

NITROGEN 


IN  SEED  SOWN 
GRAM 

IN  PLANT 
GRAM 

GAIN 
GRAM 

Clover,  2 

mos  

O.II 

O.I2 

O.OI 

Clover,  3 

mos  

O.I  I  A. 

0.156 

O.OA2 

Wheat,  2 

mos  

O.O4.1 

O.O4. 

—  o  003 

Wheat,  i 

mos  

O.OC7 

O.o6 

0.003 

Peas,     2 

mos  

O.O4.7 

O.IO 

O.O£3 

Boussingault  concluded  that  when  plants  growing  in 
a  sterile  soil  were  exposed  to  the  air,  there  was  with 
some  a  slight  gain  of  nitrogen,  but  that  the  amount 
gained  from  atmospheric  sources  was  not  sufficient  to 
feed  the  plant  and  allow  it  to  reach  full  maturity.  By 
many  these  results  were  not  accepted  as  conclusive. 

Fifteen  years  later  (1853)  Boussingault  repeated  his 


I2O 


SOILS    AND    FERTILIZERS 


experiments,  but  in  a  different  way.     The  plants  were 
now  grown  in  a  large  carboy  with  a  limited  volume  of 
air  so  as  to  cut  off  all  sources  of  com- 
bined nitrogen,  as  traces  of  ammonia, 
nitrates,  and  nitrites.     By  means  of 
a  second  glass  vessel  (B,  Fig.  30)  the 
carboy  was   kept   liberally   supplied 
with   carbon "  dioxide,   so   that   plant 
growth   would   not   be   checked    for 
lack  of  this  material.     When  experi- 
ments were  carried  on  in  this   way, 
using  a  fertile  soil,  the  plants  reached 
full  maturity ;  but  when   a   soil   free 
FIG.  30.    Plants  grown   from  nitrogen  was  used,  plant  growth 
m  Carboy.  was  soon  checked.     A  general  sum- 

mary of  this  work  is  given  in  the  following  table :  ^ 

NITROGEN 


• 

IN  SEEDS 
GRAM 

IN  PLANT 
GRAM 

Loss 
GRAM 

Dwarf  beans    .... 
Oats  

O.IOOI 
O.OIOQ 

0.0977 
O.OOQ7 

—  O.OO24 
—  O.OOI2 

White  lupines  .... 
Garden  cress    .... 

O.27IO 
O.OOI3 

0.2669 
O.OOI3 

—  O.OO4I 

These  experiments  show  that  with  a  sterilized  soil, 
and  all  sources  of  combined  atmospheric  nitrogen  cut 
off,  the  free  nitrogen  of  the  air  takes  no  part  in  the  food 
supply  of  the  plant. 


NITROGEN,    NITRIFICATION,    NITROGENOUS    MANURES       121 

In  1854  Boussingault  again  repeated  his  experiments 
on  nitrogen  assimilation.  This  time  he  grew  the  plants 
in  a  glass  case  so  constructed  that  there  was  free 
circulation  of  air  from  which  all  combined  nitrogen  had 
been  removed.  These  experiments  were  similar  to  his 
second  series,  except  the  plants  were  not  grown  in  a 
limited  volume  of  air.  The  results  obtained  showed 
that  the  free  nitrogen  of  the  air,  under  the  conditions  of 
the  experiment,  took  no  part  in  the  food  supply  of  the 
plants.  If  anything,  there  was  less  nitrogen  recovered  in 
the  dwarfed  plants  than  there  was  in  the  seed  sown. 

128.  Ville's  Results. — About  the  same  time  Ville 
carried  on  a  series  of  experiments  of  like  nature,  but  in 
a  different  way,  and  arrived  at  just  the  opposite  con- 
clusion. His  experiments  indicated  that  plants  are 
capable  of  making  liberal  use  of  the  free  nitrogen  of 
the  air  for  food  purposes.  The  directly  opposite  con- 
clusions of  Boussingault  and  Ville  led  to  a  great  deal  of 
controversy.  The  French  Academy  of  Science  took  up 
the  question,  and  appointed  a  commission  to  review  the 
work  of  Ville.  The  commission  consisted  of  six  promi- 
nent scientists.  They  reported  that  "  M.  Ville's  con- 
clusions are  consistent  with  his  labor  and  results."39 

129.  Work  of  Lawes  and  Gilbert. — A  little  later 
Lawes  and  Gilbert  carried  on  such  extensive  experi- 
ments under  a  variety  of  conditions  as  to  remove  all 
doubt  regarding  the  plants'  source  of  nitrogen.  Plants 


122  SOILS    AND    FERTILIZERS 

were  grown  in  sterilized  soils,  in  prepared  pumice  stone, 
and  in  soils  with  a  limited  quantity  of  nitrogen  beyond 
that  contained  in  the  seed.  Different  kinds  of  plants 
were  experimented  with.  The  work  was  carried  on  with 
the  utmost  care  and  with  apparatus  so  constructed  as  to 
eliminate  all  disturbing  factors.  The  results  in  the 
aggregate  clearly  show  that  plants,  when  acting  in  a 
sterile  medium,  are  unable  to  make  use  of  the  free 
nitrogen  of  the  air  for  the  production  of  organic 
matter.39 

130.  Atwater's  Experiments.  —  Atwater   carried   on 
similar  experiments  in  this  country.41     His  results  in- 
dicate that  when  seeds  germinate  they  lose  a  small  part 
of  their  nitrogen,  and  when  legumes  are  grown  in  a 
sterile  soil,  but  are  subsequently  exposed  to  the  air,  a 
fixation  of  nitrogen  may  occur.    He  ascribed  this  gain  to 
micro-organisms  or  other  agencies. 

131.  Field  and  Laboratory  Tests.  —  By  a  five  years' 
rotation  of  clover  and  other  leguminous  plants,  Lawes 
and    Gilbert  found    a   soil    gained    from    200    to    400 
pounds  of  nitrogen  per  acre,  in  addition  to  that  removed 
in  the  crop,  while  land  which  produced  wheat  contin- 
uously, gradually  lost   nitrogen.     The  amount  in   the 
subsoil  remained  nearly  the  same.     These  facts  plainly 
indicated  that  crops  like  clover  have  the  power  of  gain- 
ing nitrogen  from   unknown    sources.     The  results  of 
prominent  German  agriculturists  led  to  the  same  con- 


NITROGEN,    NITRIFICATION,    NITROGENOUS    MANURES      123 

elusion.  It  was  known  that  wheat  grown  after  clover 
gave  as  good  results  as  when  nitrogenous  manures  were 
used,  but  for  many  years  this  was  unexplained. 

Laboratory  experiments  with  sterilized  soils  do  not 
represent  the  normal  conditions  of  growing  crops,  where 
all  of  the  bacteriological  agencies  of  the  soil,  the  air, 
and  the  plant  are  free  to  act.  Experiments  show  that 
these  agencies  have  an  important  bearing  upon  plant 
growth. 

In  the  work  of  the  different  investigators  prior  to 
1888,  plants  were  grown  mainly  in  sterilized  soils,  and 
under  such  conditions  they  were  unable  to  make  use  of 
the  free  nitrogen  of  the  air,  except  when  the  soils  were 
subsequently  inoculated  from  the  air. 

132.  Hellriegel's  Experiments.  —  Hellriegel  grew  le- 
guminous plants  in  nitrogen-free  soils.  One  set  of 
plants  was  watered  with  distilled  water,  while  another 
had  in  addition  small  amounts  of  leachings  from  an  old 
loam  field.  The  plants  watered  with  distilled  water 
alone  made  but  little  growth,  while  those  watered  with 
the  loam  leachings  reached  full  maturity  and  contained 
something  like  a  hundred  times  more  nitrogen  than  was 
in  the  seed  sown.  The  dark  green  color  also  was 
developed,  showing  the  presence  of  a  normal  amount  of 
chlorophyll.  The  roots  of  the  plants  had  well-formed 
swellings  or  nodules,  while  those  that  were  watered  with 
distilled  water  alone  had  none.  The  loam  leachings 
contained  only  a  trace  of  nitrogen.42 


124 


SOILS   AND    FERTILIZERS 


133.  Experiments  of  Wilfarth.  —  Experiments  by 
Wilfarth  give  more  exact  data  regarding  the  amount 
of  nitrogen  taken  from  the  air.  Two  plots  of  lupines 
were  grown ;  one  was  watered  with  distilled  water,  while 
the  other  received  in  addition  a  small  amount  of  leach- 
ings  from  an  old  lupine  field. 


WATERED  WITH  DISTILLED  WATER 

WATERED  WITH  DISTILLED  WATER 
AND  SOIL  LEACHINGS 

Dry  matter 
Grams 

Nitrogen 
Grams 

Dry  matter 
Grams 

Nitrogen 
Grams 

0.919 
O.8OO 
0.921 

0015 
O.OI4 
0.013 

4472 
45.61 
44.48 

1.099 

I-I53 
I.I95 

1.  02  1 

O.OI3 

42.45 

1-337 

These  experiments  have  been  verified  by  many  other 
investigators  until  the  fact  has  been  established  that 
leguminous  plants  may,  through  the  agency  of  micro- 
organisms, make  use  of  the  free  nitrogen  of  the  air. 
When  legumes  were  grown  in  closed  vessels  and  the  air 
was  analyzed,  it  was  found  that  there  was  a  loss  of 
nitrogen  from  the  air  proportional  to  that  gained  by  the 
plants. 

The  work  of  Hellriegel  was  not  accidental,  but  the 
result  of  careful  and  systematic  investigation.  As  early 
as  1863  he  observed  that  clover  would  develop  along  the 
roadway  in  sand  in  which  there  was  scarcely  a  trace  of 
combined  nitrogen. 


NITROGEN,    NITRIFICATION,    NITROGENOUS    MANURES      12$ 

134.  Composition  of  Root  Nodules.  —  The  root  nodules 
referred  to   are  particularly  rich  in  nitrogen.     In  one 
experiment,  the  light-colored  and  active  ones  contained 
5.55  per  cent,  while  those  dark-colored  and  older  con- 
tained 3.21  per  cent,  and  all  the  nodules  of  the  root, 
both  active  and  inactive,  contained  4.60  per  cent  nitro- 
gen.    The  root  itself  contained  2.21  per  cent.43 

The  root  nodules  also  contain  definite  and  character- 
istic micro-organisms,  and  it  was  the  spores  of  these  or- 
ganisms that  were  in  the  soil  extract  in  both  Hellriegel's 
and  Wilfarth's  experiments.  In  the  sterilized  soils  they 
were  not  present.  These  organisms  found  in  root  nod- 
ules are  the  essential  agents  which  aid  in  the  fixation  of 
the  free  nitrogen  of  the  air,  and  in  its  ultimate  use  as 
plant  food.  The  nitrogen  assimilated  by  the  micro- 
organisms in  the  nodules  of  the  legumes  is  in  part  ap- 
propriated by  the  crop,  which  unaided  is  incapable  of 
making  use  of  the  free  nitrogen  of  the  air. 

135.  Nitrogen  in  the  Root   Nodules   returned   to  the 
Soil.  —  Ward  has  shown  that  when  clover  roots  decay, 
the  organisms  and  nitrogen  present  in  the  nodules  are 
distributed  within  the  soil.38     Hence,  whenever  a  legu- 
minous  crop  is   raised,   nitrogen   is  added  to  the  soil 
instead  of  being  taken  away,  as  in  the  case  of  a  grain 
crop.     The  amount  of  nitrogen  returned  to  the  soil  by 
a  leguminous  crop  as    clover  varies  with   the  growth 
of  the  crop.     In  the  roots  of  a  clover  crop  a  year  old 
there  are  from  20  to  30  pounds  of  nitrogen  per  acre, 


126  SOILS   AND   FERTILIZERS 

while  in  the  roots  and  culms  of  a  dense  clover  sod, 
two  or  three  years  old,  there  may  be  100  pounds  or 
more  of  nitrogen,  not  including  that  which  has  been 
added  to  the  soil  by  the  accumulative  action  of  the  crop. 
Peas,  beans,  lucern,  cow  peas,  and  all  legumes  possess 
the  power  of  fixing  the  free  nitrogen  of  the  air  by  means 
of  micro-organisms.  The  micro-organisms  associated  with 
one  species,  as  clover,  differ  from  those  associated  with 
another,  as  lucern.  The  amount  of  nitrogen  which  the 
various  legumes  return  to  the  soil  is  variable. 

Hellriegel's  results  are  of  the  greatest  importance  to 
agriculture,  because  they  show  how  the  free  nitrogen  of 
the  air  can  be  utilized  indirectly  as  food  by  crops  unable 
to  appropriate  it  for  themselves. 

THE  NITROGEN  COMPOUNDS  OF  THE  SOIL 

136.  Origin  of  the  Soil  Nitrogen.  —  The  nitrogen  of 
the  soil  is  derived  chiefly  from  the  accumulated  remains 
of  animal  and  vegetable  matter.  The  original  source 
of  the  soil  nitrogen,  that  is,  the  nitrogen  which  furnished 
food  to  support  the  vegetation  from  which  our  present 
stock  of  soil  nitrogen  is  obtained,  was  probably  the  free 
nitrogen  of  the  air.  All  of  the  ways  in  which  the  free 
nitrogen  of  the  air  has  been  made  available  to  plants  of 
higher  orders  which  require  combined  nitrogen  are  not 
known.  It  is  supposed,  however,  that  this  has  been 
brought  about  by  the  workings  of  lower  forms  of  plant 
life,  and  by  micro-organisms.  Whatever  these  agencies, 
they  do  not  appear  to  be  active  in  a  soil  under  high  cul- 


FIG.  31. 


Clover  Roots  showing  Nodules  which  contain  Nitrogen-assimilating 
Organisms. 


NITROGEN,    NITRIFICATION,    NITROGENOUS   MANURES       I2/ 

tivation,  because  the  tendency  of  ordinary  cropping  is  to 
reduce  the  supply  of  soil  nitrogen. 

137.  Organic  Nitrogen  of  the  Soil.  —  In  ordinary  soils 
the  nitrogen  is  present  mainly  in  organic  forms  com- 
bined with  the  carbon,  hydrogen,  and  oxygen  as  humus, 
and  to  a  less  extent  with  the  mineral  elements,  forming 
nitrates  and  nitrites.     The  organic   forms  of  nitrogen, 
it  is  generally  considered,  are  incapable  of  supplying 
plants  with  nitrogen  for  food  purposes  until  the  process 
known  as  nitrification  has  taken  place.     The  nitrogenous 
organic  compounds  in  cultivated  soils  are  derived  mainly 
from  the  undigested  protein  compounds  of  manure  and 
from  the  nitrogenous  compounds  in  crop  residues,  and 
are  present  mainly  as  insoluble  proteids.85     When  de- 
composition   occurs,  amides,   organic    salts,  and    other 
allied  bodies  are  without  doubt  produced   as  interme- 
diate products  before  nitrification  takes  place.     The  or- 
ganic nitrogen  of  the  soil  may  be  present  in  exceedingly 
inert  forms  similar  to  that  in  leather,  as  in  many  peaty 
soils  where  there  are  large  amounts  of  inactive  organic 
compounds  rich  in  nitrogen.     In  other  soils  the  nitrogen 
is  less  complex.     The  organic  nitrogen  of  the  soil  may 
vary  in  complexity  from  forms,  like  the  nitrogen  of  urea, 
which  readily  undergo  nitrification,  to  forms  like  that  in 
peat,  which  nitrify  with  difficulty. 

138.  Amount   of   Nitrogen    in   Soils.  —  The    fertility 
of  any  soil  is  dependent,  to  a  great  extent,  upon  the 


128  SOILS    AND    FERTILIZERS 

amount  and  form  of  its  nitrogen.  In  soils  of  the 
highest  fertility  there  is  usually  present  from  0.2  to 
0.3  per  cent  of  total  nitrogen,  equivalent  to  from 
7000  to  10,000  pounds  per  acre  to  the  depth  of  one 
foot.  Many  soils  of  good  crop-producing  power  contain 
as  low  as  o.i  2  per  cent.  There  is  usually  two  or  three 
times  more  nitrogen  in  the  surface  soil  than  in  the  sub- 
soil. In  sandy  soils  which  have  been  allowed  to  decline 
in  fertility,  there  may  be  less  than  0.04  per  cent.  Of 
the  total  nitrogen  in  soils  there  is  rarely  more  than  2 
per  cent  at  any  one  time  in  forms  available  as  plant 
food.44  A  soil  with  5000  pounds  of  total  nitrogen  per 
acre  may  contain  less  than  100  pounds  of  available  nitro- 
gen soluble  in  the  soil  water,  of  which  only  a  part  is 
assimilated  by  the  roots  of  crops.  Hence  it  is  that  a 
soil  may  contain  a  large  amount  of  total  nitrogen,  and 
yet  be  deficient  in  available  nitrogen. 

139.   Amount  of  Nitrogen   removed  in    Crops.  —  The 

amount  of  nitrogen  removed  in  crops  ranges  from  25  to 
100  pounds  per  acre,  depending  upon  the  nature  of  the 
crop.  It  does  not  necessarily  follow  that  the  crop  which 
removes  the  largest  amount  of  nitrogen  leaves  the  land 
in  the  most  impoverished  condition.  Wheat  and  other 
grains,  while  they  do  not  remove  so  much  in  the  crop, 
leave  the  soil  more  exhausted  than  if  other  crops  were 
grown.  This,  as  will  be  explained,  is  caused  by  the  loss 
of  nitrogen  from  the  soil  in  other  ways  than  through  the 
crop. 


NITROGEN,    NITRIFICATION,    NITROGENOUS   MANURES 


POUNDS  OF 
NITROGEN  PER 
ACRE  REMOVED 

IN   CROP38 


Wheat,  20  bushels 25 

Straw,  2000  pounds 10 

Total 35 

Barley,  40  bushels 28 

Straw,  3000  pounds 12 

Total 40 

Oats,  50  bushels  .     .     .     .  - 35 

Straw,  3000  pounds 15 

Total 50 

Flax,  15  bushels 39 

Straw,  1800  pounds 15 

Total 54 

Potatoes,  1 50  bushels 40 

Corn,  65  bushels 40 

Stalks,  3000  pounds 35 

Total 75 


140.  Nitrates  and  Nitrites.  —  Nitrogen  in  the  form  of 
nitrates  and  nitrites  varies  from  mere  traces  to  150 
pounds  per  acre.  Soils  with  large  amounts  of  nitroge- 
nous humus  and  lime  may  contain  for  short  periods  as 
high  as  300  pounds  of  nitrates  and  1 5  pounds  of  nitrites, 
calculated  as  sodium  salts.  Some  soils  contain  more 
nitrates  than  are  utilized  by  crops  as  food,  and  plants 
may  assimilate  more  than  they  can  convert  into  protein. 


I3O  SOILS     AND     FERTILIZERS 

Wheat,  corn,  and  other  crops  grown  on  rich  soils  may 
contain  both  nitrates  and  nitrites  as  normal  constituents. 
King  reports  nitrates  in  the  growing  crop  in  much  larger 
amounts  than  in  the  soil  water.  As  the  crop  matures 
the  nitrate  content  of  the  plant  declines.  Calcium  ni- 
trate is  the  usual  form,  especially  in  soils  which  are 
sufficiently  supplied  with  calcium  carbonate  to  allow 
nitrification  to  progress  rapidly.  Nitrates  and  nitrites 
are  the  most  valuable  forms  of  nitrogen  for  plant  food. 
Both  are  produced  from  the  organic  nitrogen  of  the  soil. 
A  nitrate  is  a  compound  composed  of  a  base  element  as 
sodium,  potassium,  or  calcium,  combined  with  nitrogen 
and  oxygen.  A  nitrite  contains  less  oxygen  than  a  nitrate. 
Potassium  nitrate,  KNO3,  sodium  nitrate,  NaNO3, 
and  calcium  nitrate,  Ca(NO3)2  are  the  nitrates  which 
are  of  most  importance  in  agriculture.  The  nitrites,  as 
potassium  nitrite,  KNO2,  are  present  to  a  less  extent 
than  the  nitrates.  Nitrates  and  nitrites  are  found  in 
surface  well  waters  contaminated  with  animal  and  vege- 
table matter.  Many  well  waters  possess  some  material 
value  as  a  fertilizer  on  account  of  the  nitrates,  nitrites, 
and  decaying  animal  and  vegetable  matters  which  they 
contain. 

141.  Ammonium  Compounds  of  the  Soil.  —  The  am- 
monium compounds  in  a  soil  are  usually  less  in  amount 
than  the  nitrates  and  nitrites.  The  sources  are  rain 
water  and  the  organic  matter  of  the  soil.  The  am- 
monium compounds  are  all  soluble  and  readily  undergo 


NITROGEN,    NITRIFICATION,    NITROGENOUS   MANURES       131 

fixation.  See  Chapter  VI.  They  cannot  accumulate 
in  arable  soils,  because  of  nitrification  and  fixation. 
Usually  they  are  to  be  found  in  surface  well  waters. 
In  the  soil,  the  ammonium  compounds  are  acted  upon 
by  nitrifying  organisms,  and  nitrites  and  nitrates  are 
formed.  Such  compounds  as  ammonium  chloride  or 
ammonium  carbonate,  if  present  in  a  soil  in  excessive 
amounts,  will  destroy  vegetation  in  a  way  similar  to 
the  alkaline  compounds  in  alkaline  soils,  but  in  small 
amounts  they  are  beneficial. 

142.  Nitrogen  in  Rain  Water  and  Snow.  —  Ordinarily 
the  nitrogen  which  is  annually  returned  to  the  soil  in 
the    form  of   ammonium  compounds  dissolved  in  rain 
water  and  snow  is  equivalent  to  from  2  to  3    pounds 
per  acre.     At  the  Rothamsted  Experiment  Station  the 
average    amount   for   eight   years   was   3.37   pounds.44 
When   a   soil   is  rich  in  nitrogen  the  gain  from  rain 
and  snow  is  only  a  partial  restoration  of  that  which 
has  been  given  off  from  the  soil  to  the  air  or  lost  in  the 
drain  waters.     The  principal  forms  of  the  nitrogen  in 
rain  water  are  ammonium  carbonate  and  nitrates  and 
nitrites,  present  in  the  air  to  the  extent  of  about  22  parts 
per  million  parts  of  air. 

143.  —  Ratio  of  Nitrogen  to  Carbon  in  the  Organic 
Matter  of  Soils. —  In  some  soils  the  organic  matter  is 
more  nitrogenous  than  in  others.     In  those  of  the  arid 
regions  the  humus  contains  from  15  to  20  per  cent  of 


132  SOILS    AND    FERTILIZERS 

nitrogen,  while  in  soils  from  the  humid  regions  there  is 
from  4  to  6  per  cent.45  In  some  soils  the  ratio  of  nitro- 
gen to  carbon  is  I  to  6,  while  in  others  it  may  be  I  to 
1 8,  or  more.  That  is,  in  the  organic  matter  of  some  soils 
there  is  I  part  of  nitrogen  to  6  parts  of  carbon,  while  in 
others  the  organic  matter  contains  I  part  of  nitrogen  to 
1 8  parts  of  carbon.  In  a  soil  where  there  exists  a  wide 
ratio  between  the  nitrogen  and  carbon,  it  is  believed  the 
conditions  for  supplying  crops  with  available  nitrogen 
are  unfavorable. 

144.  Losses  of  Nitrogen  from  Soils.  —  When  a  soil 
rich  in  nitrogen  is  cultivated  for  a  number  of  years  ex- 
clusively to  grain,  there  is  a  loss  of  nitrogen  exceeding 
that  removed  in  the  crop,  caused  by  the  rapid  oxida- 
tion of  the  organic  matter  of  the  soil.  Experiments 
show  that  when  a  prairie  soil  of  average  fertility  is 
cultivated  continually  to  grain,  for  every  25  pounds  of 
nitrogen  removed  in  the  crop  there  is  a  loss  of  about 
1 50  pounds  due  to  the  destruction  of  the  organic  mat- 
ter.18 In  general,  any  system  of  cropping  which  keeps 
the  soil  continually  under  the  plow  results  in  decreas- 
ing the  nitrogen.  When  a  soil  is  rich  in  nitrogen  the 
greatest  losses  occur;  when  poor  in  nitrogen  there  is 
relatively  less  loss.  When  a  soil  rich  in  nitrogen  is 
given  arable  culture,  oxidation  of  the  organic  matter  and 
losses  of  nitrogen  take  place  rapidly.  The  longer  a 
soil  is  cultivated,  the  slower  the  oxidation  of  the  humus 
and  relative  loss  of  nitrogen. 


NITROGEN,'  NITRIFICATION,    NITROGENOUS    MANURES       133 


Dyer  has  calculated  the  income  and  outgo  of  ni- 
trogen from  manured  and  unmanured  plots  at  the 
Rothamsted  Station  for  a  period  of  fifty  years.  "  Of 
the  total  10,000  pounds  of  nitrogen  estimated  to  have 
been  supplied,  then,  we  find  (in  round  numbers)  that 
1600  pounds  have  been  recovered  in  the  increased 
crops  and  that  about  2500  pounds  are  found  in  the 
surface  soil,  leaving  5900  (or,  in  round  numbers, 
6000)  pounds  to  be  accounted  for  otherwise.  It  is 
clear,  therefore,  in  spite  of  the  notable  surface  ac- 
cumulation, but  little  of  the  large  quantities  of  nitrogen 
supplied  in  the  dung  and  not  returned  in  crops  is  to 
be  found  in  the  subsoil.  The  greater  part  of  it  has 
disappeared  either  as  nitrates  in  the  drainage  or  per- 
haps, and  probably  largely,  by  fermentative  processes 
yielding  free  nitrogen."68 

145.  Gain  of  Nitrogen  in  Soils.  —  Lawes  and  Gilbert 
found  a  gain  of  nitrogen  when  land  was  permanently 
covered  with  vegetation.44  Pastures  and  meadows 
contain  more  than  cultivated  land  of  similar  character. 


AGE  OF  PASTURE 
YEARS 

NITROGEN 
PER  CENT 

Arable  land     ........... 

O.I4. 

Barn-field  pasture     

8 

O.I  CI 

Apple-tree  pasture   

18 

O.I  74. 

Meadow      

21 

O.2O4. 

Meadow      

•JO 

O.24.I 

134  SOILS   AND    FERTILIZERS 

After  deducting  the  amount  of  nitrogen  in  the  ma- 
nure  added  to  the  meadow  land,  the  annual  gain  of  nitro- 
gen was  more  than  44  pounds  per  acre. 

If  a  soil  is  properly  manured  and  cropped,  the 
nitrogen  may  be  increased.  A  five-course  rotation  of 
small  grains,  clover,  and  corn  (manured)  will  generally 
leave  the  soil  at  the  end  of  the  period  of  rotation  in 
better  condition  as  regards  nitrogen  than  at  the  be- 
ginning. 

At  the  Minnesota  Experiment  Station  where  wheat, 
corn,  barley,  and  oats  were  grown  continuously  for 
twelve  years,  a  loss  of  about  2000  pounds  per  acre  of 
nitrogen  was  sustained ;  from  |-  to  f  of  the  nitrogen  be- 
ing lost  in  various  ways  and  not  utilized  as  plant  food.85 
In  experiments  covering  ten-year  periods,  it  was  found 
that  the  five-year  rotations,  in  which  clover  formed  an 
essential  part,  resulted  in  a  slight  increase  in  the  nitro- 
gen content  of  the  soil,  —  about  300  pounds  per  acre  in 
excess  of  that  removed  in  the  crops.  When  timothy 
and  non-legumes  were  substituted  for  clover,  "a  loss 
of  nitrogen  from  the  soil  occurred,  but  the  carbon 
(humus)  content  was  maintained ;  the  loss  of  nitrogen 
from  the  soil  only  slightly  exceeding  that  removed  by 
the  crops."  m 

It  is  to  be  regretted  that  in  the  cultivation  of  large 
areas  of  land  to  staple  crops,  as  wheat,  corn,  and  cotton, 
the  methods  of  cultivation  followed  are  such  as  to  de- 
crease the  nitrogen  content  and  crop-producing  power 
of  the  soil  when  this  might  be  prevented. 


NITROGEN,    NITRIFICATION,    NITROGENOUS    MANURES      135 

NITRIFICATION 

146.  Former    Views    regarding    Nitrification. — The 
presence  of  nitrates  and  nitrites  in  soils  was  formerly 
accounted  for  by  oxidation.     The  theory  was  held  that 
the  production  of  nascent  nitrogen  by  the  decomposition 
of  organic  matter  caused  a  union  between  the  oxygen 
of  the  air  and  the  nitrogen  of  the  organic  matter.     Fer- 
mentation studies  by  Pasteur  led  him  to  suggest  in  1862 
that   possibly  the  formation  of  nitric  acid  in  the  soil 
might  be  due  to  fermentation.     It  was,  however,  fifteen 
years  later  before  the  French  chemists,  Schlosing  and 
Miintz,  established  the   fact  that   nitrification   is   pro- 
duced by  a  living  organism.     They  passed  diluted  sew- 
age through  a  glass  tube  filled  with  sand  to  which  a 
little  lime  was  added.     The  first   portions   of   sewage 
contained  nitrogen  in  the  form  of  ammonia,  but  after  a 
number  of  days  nitrates  appeared,  and  the  ammonia 
diminished.     When   the   soil  was  treated  with  chloro- 
form vapor,  nitrates  ceased  to  be  formed ;  when  fresh 
garden  soil  was  added,  nitrates  again  appeared  in  the 
leachings.     The  bacteria  were  destroyed  by  the  chloro- 
form, and  the  medium  was  reseeded  from  the  garden 
soil. 

147.  Nitrification  caused  by  Micro-organisms.  —  Nitri- 
fication is  the  process  by  which  nitrates  and  nitrites  are 
produced  in  soils  by  the  workings  of  organisms.     Nitri- 
fication results  in  changing  the  complex  organic  nitro- 


136 


SOILS   AND    FERTILIZERS 


gen  of  the  soil  to  the  form  of  nitrates  or  nitrites. 
Broadly  speaking,  it  is  the  process  by  which  the  inert 
nitrogen  of  the  soil  is  rendered  available  as  crop  food. 
The  organisms  which  carry  on  the  work  of  nitrification 
were  first  isolated  and  studied  by  Winogradsky. 

148.   Conditions  Necessary  for  Nitrification  are  : 

1.  Presence  of  the  nitrifying  organisms  and  food  for 
them. 

2.  A  supply  of  oxygen. 

3.  Moisture. 

4.  A  favorable  temperature. 

5.  Absence  of  strong  sunlight. 

6.  The  presence  of  some  basic  compound. 

In  order  to  allow  nitrification  to  proceed,  all  of  these 
conditions  must  be  satisfied.  The  process  is  frequently 
checked  because  some  of  the  conditions,  as  presence  of 
a  basic  compound,  are  unfulfilled. 


FIG.  32.     Nitrous  Acid  Organisms.     (After  Winogradsky.) 


NITROGEN,    NITRIFICATION,    NITROGENOUS    MANURES       137 

149.  Food  for  the  Nitrifying  Organisms.  —  All  living 
organisms  require  food,  and  one  of  the  food  require- 
ments of  the  nitrifying  organism  is  a  supply  of  phos- 
phates and  other  minerals.  In  the  absence  of  phos- 
phoric acid,  nitrification  cannot  take  place.  The 
change  which  the  phosphoric  acid  undergoes  in  serving 


**  ^^s^^^MKm^R 


FIG.  33.     Nitric  Acid  Organism.     (After  Winogradsky.) 

as  food  for  the  nitrifying  organism  is  unknown,  but  it 
doubtless  makes  the  phosphoric  acid  more  available  as 
plant  food.91  The  principal  organic  food  of  the  nitrify- 
ing organism  is  the  organic  matter  of  the  soil,  and  it  is 
only  when  organic  matter  is  incorporated  with  soil  that 
it  can  serve  as  food  for  the  nitrifying  organism.  In  the 
presence  of  a  large  amount  of  organic  matter,  as  in  a 
manure  pile,  nitrification  does  not  take  place.  It  occurs 
only  when  the  organic  matter  is  largely  diluted  with 
soil.  Under  favorable  conditions,  nitrifying  organisms 


138  SOILS   AND   FERTILIZERS 

may  secure  all  of  their  food  in  inorganic  forms ;  that  is, 
nitrification  may  take  place  in  the  absence  of  organic 
matter,  provided  the  proper  mineral  food  be  supplied. 
When  growth  under  such  conditions  takes  place  the 
organisms  assimilate  carbon  from  the  combined  carbon 
of  the  air,  and  produce  organic  carbon  compounds.  An 
organism,  working  in  the  absence  of  sunlight  and  un- 
provided with  chlorophyll,  may  construct  organic  com- 
pounds containing  nitrogen  and  designated  bacterial 
protein.44  Nitrification  in  the  absence  of  nitrogenous 
organic  matter  is  of  too  limited  a  character  to  supply 
growing  crops  with  all  of  their  available  nitrogen.  For 
general  crop  production  the  organic  matter  of  the  soil 
is  the  source  of  the  nitrogen  which  undergoes  the  nitri- 
fication process,  and  which  furnishes  food  for  the  nitrify- 
ing organisms. 

150.  Oxygen  Necessary  for  Nitrification.  —  The  second 
requirement  for  nitrification  is  an  adequate  supply  of 
oxygen.  The  nitrifying  organism  belongs  to  that  class 
of  ferments  (aerobic)  which  requires  oxygen  for  exist- 
ence. Oxygen  is  present  as  one  of  the  elements  in  the 
final  product  of  nitrification  as  calcium  nitrate,  Ca(NO3)2. 
In  the  absence  of  oxygen,  nitrification  is  checked. 
When  soils  are  saturated  with  water,  the  process  can- 
not go  on  for  want  of  oxygen.  The  formation  of  a 
hard,  dry  crust  in  soils  also  checks  nitrification.  Cultiva- 
tion, particularly  of  clay  soils,  favors  nitrification  by 
increasing  the  supply  of  oxygen  in  the  soil. 


NITROGEN,    NITRIFICATION,    NITROGENOUS    MANURES      139 

151.  Moisture  Necessary  for  Nitrification.  —  Nitrifica- 
tion cannot  take  place  in  a  soil  deficient  in  moisture ; 
as  in  all  fermentation  processes,  moisture  is  necessary 
for  the  chemical  changes  to  occur.     In  a  very  dry  time 
nitrification  is  arrested  for  want  of  water.     Water  is  as 
necessary  to  the  growth  and  development  of  the  living 
organism  which  carries  on  the  work  of  nitrification  as 
it  is  to  the  life  of  a  plant  of  higher  order. 

152.  Temperatures  Favorable  for  Nitrification.  —  The 

most  favorable  temperatures  for  nitrification  are  between 
12°  C.  (54°  F.)  and  37°  C.  (99°  R).  It  may  take  place 
at  as  low  a  temperature  as  3°  or  4°  C.  (37°  and  39°  F); 
at  50°  C.  (122°  F.)  it  is  feeble ;  while  at  55°  C.  (130°  F.) 
there  is  no  action.44  In  northern  latitudes  nitrification 
is  checked  during  the  winter,  while  in  southern  latitudes 
this  change  takes  place  throughout  the  entire  year.  As 
a  result,  many  soils  in  southern  latitudes  contain  less 
nitrogen  than  soils  in  northern  latitudes  where  forma- 
tion and  leaching  of  nitrates  are  checked  by  climatic 
conditions.  Crops  which  require  their  nitrogen  early 
in  the  growing  season  are  frequently  placed  at  a  dis- 
advantage because  there  is  less  available  nitrogen  in 
the  soil  at  that  time  than  later. 

153.  Strong  Sunlight  checks  Nitrification.  —  Nitrifica- 
tion cannot  take  place  in  strong  sunlight;  it  prevents 
the  action  of  all  organisms  of  this  class.     In  fallow  land 
there  is  no  nitrification  at  the  surface,  but  immediately 


I4O  SOILS    AND    FERTILIZERS 

below  where  the  sunlight  is  excluded  by  the  surface 
soil  it  is  most  active.  In  a  corn  field  it  is  more  active 
than  in  a  compacted  fallow  field. 

154.  Base-forming  Elements  Essential  for  Nitrification. 
—  The  presence  of  some  base-forming  element  to  com- 
bine with  the  nitric  acid  produced  is  a  necessary  con- 
dition for  nitrification,   and  for  this   purpose   calcium 
carbonate  and  sodium  and  potassium  compounds  are 
particularly  valuable.     The  absence  of  alkaline  salts  is 
one  of  the  frequent  causes  of  non-nitrification.     In  acid 
soils   the  process  is  checked  for  the  want  of  proper 
basic   material.      The   organisms   which   carry  on   the 
work   cannot   exist   where   there   are   strong   acids  or 
alkalies,  consequently  in  such  soils  nitrification  cannot 
take  place. 

155.  Nitrous  Acid  Organisms.  —  There   are   at  least 
two    nitrifying   organisms   in   the   soil :    one   produces 
nitrates  and  the  other  nitrites  or  nitrous  acid.     It  has 
been  shown  that  the  nitrification  process  takes  place  in 
two  stages:  first  nitrites  are  produced  by  the  nitrous 
organism,  and   then  the  process  is  completed  by  the 
nitric   organism.     Warington   says   that  "both   organ- 
isms are  present  in  the  soil  in  enormous  numbers,  and 
the  action  of  the  two  organisms  proceeds  together,  as 
the  conditions   are  favorable    to   both."      As   a  result 
of  the  workings  of  the  nitrous  acid  organism,  nitrites 
are  formed,  and  these  are  acted  upon  by  the  nitric  acid 


NITROGEN,    NITRIFICATION,    NITROGENOUS    MANURES       14! 

organism  and  changed  into  nitrates.  Nitrites  exist  in 
soils  as  transition  products,  the  amount  present  in  fer- 
tile soils  being  less  than  one  part  per  million  of  soil. 

156.  Ammonia-producing  Organisms.  —  There  are  also 
present   in  the  soil   organisms  which  have  the  power 
of  producing  ammonia  from  proteid  bodies.     The  am- 
monium compounds  produced  are  acted  upon  by  the 
nitrifying    organisms    and    readily    undergo     nitrifica- 
tion.46'68    When  oxidation  of  the  protein  is  rapid,  nitro- 
gen may  be  liberated  and  lost. 

157.  Denitrification  is  just  the  reverse  of  the  nitri- 
fication process,  and  is  the  result  of  the  workings  of 
a  class   of   organisms   which  feed   upon   the   nitrates, 
forming  free  nitrogen  which  is  liberated  as  a  gas.     One 
of  the  conditions  for  denitrification  is   absence  of  air, 
as  these  organisms  belong  to  the  anaerobic  class.     De- 
nitrification  occurs   in    soils  saturated  with  water,  and 
where  the  soil  is  compacted  so  that  air  is  practically 
excluded.47- a 

158.  Number  and  Kinds  of  Organisms  in  Soils. — In 

addition  to  the  micro-organisms  which  carry  on  the 
work  of  nitrification,  denitrification,  and  ammonifi cation, 
there  are  a  great  many  others,  some  of  which  are  bene- 
ficial while  others  are  injurious  to  crop  growth.  It  has 
been  estimated  that  in  a  gram  of  an  average  sample  of 
soil  there  are  from  60,000  to  500,000  beneficial  and 
injurious  micro-organisms.48  There  are  produced  from 


142  SOILS   AND   FERTILIZERS 

many  crop  residues,  by  injurious  ferments,  chemical 
products  which  may  be  destructive  to  crop  growth. 
Flax  straw,  for  example,  when  it  decays  in  the  soil, 
forms  chemical  products  which  are  destructive  to  a 
succeeding  flax  crop. 

A  moist  soil,  rich  in  organic  matter,  and  containing 
various  salts,  may  form  the  medium  for  the  propagation 
of  many  classes  of  organisms.  Sewage-sick  soils,  clover- 
sick  soils,  and  flax-diseased  lands  are  all  the  result  of 
bacterial  diseases.  Many  of  the  organisms  which  are 
the  cause  of  such  diseases  as  typhoid  fever  and  cholera 
may  propagate  and  develop  in  a  moist  soil  under  certain 
conditions,  and  then  find  their  way  through  drain  water 
into  surface  wells,  and  cause  these  diseases  to  spread. 

159.  Products  formed  by  Soil  Organisms.  —  In  con- 
sidering the  part*  which  micro-organisms  take  in  plant 
growth,  as  well  as  in  all  similar  processes,  there  are  two 
important  phases  :  (i)  the  action  of  the  organism  itself, 
and  (2)  the  chemical  action  of  the  product  of  the  or- 
ganism. In  the  case  of  nitrification,  the  action  of  the 
organism  brings  about  a  change  in  the  composition  of 
the  organic  matter  of  soils  producing  nitric  acid,  which 
is  merely  a  product  formed  as  a  result  of  the  action  of 
the  organism.  The  nitric  acid  then  acts  upon  the  soil, 
producing  nitrates.  In  soils  rich  in  organic  matter  the 
fermentation  changes,  which  take  place  during  humifi- 
cation,  result  in  the  production  of  acid  products.  This 
is  simply  the  result  of  the  action  of  the  ferments.  The 


NITROGEN,    NITRIFICATION,    NITROGENOUS   MANURES       143 

acids  then  act  upon  the  soil  bases  and  produce  humates 
or  organic  salts.  In  many  fermentation  changes  there 
is  first  the  production  of  some  chemical  compound,  and 
then  the  action  of  this  compound  upon  other  bodies.  In 
rendering  plant  food  available,  as  in  humification  and 
nitrification,  it  is  the  final  and  not  the  first  product  of 
the  organism,  which  is  of  value  as  plant  food. 

160.  Inoculating  Soils  with  Organisms.  —  In  growing 
leguminous  crops  on  soils  where  they  have  never  before 
been  produced,  it  has  been  proposed  to  supply  the 
essential  organisms  which  assist  the  crops  to  obtain 
their  nitrogen.  For  example,  if  clover  is  grown  on  new 
land,  the  soil  may  not  contain  the  organisms  which 
assist  in  the  assimilation  of  nitrogen  and  which  are 
present  in  the  root  nodules  of  the  plant.  If  these 
organisms  are  supplied,  better  conditions  for  growth 
exist.  Some  soils  are  benefited  by  inoculation,  while 
others  are  not.  Frequently  the  failure  successfully  to 
grow  legumes  is  due  to  other  causes,  as  poor  seed,  poor 
physical  condition  of  the  soil,  lack  of  mineral  plant 
food,  and  adverse  climatic  conditions  rather  than  to  a 
lack  of  the  necessary  nitrogen  fixing-bacteria.68 

In  old  soils  where  the  process  of  nitrification  is 
feeble,  it  has  been  proposed  to  inoculate  the  soils  with 
more  active  forms  of  bacteria  so  as  to  make  the  inert 
humus  nitrogen  more  available  as  plant  food.  In  order 
to  secure  the  best  results  from  inoculation,  suitable 
food  must  be  supplied  for  the  organisms,  and  any  ad- 


144  SOILS   AND    FERTILIZERS 

verse  condition,  as  excess  of  acids  or  alkalies,  must 
be  corrected.  Most  soils  contain  the  requisite  organ- 
isms, but  frequently  they  are  unable  to  do  their  work 
because  of  unfavorable  conditions,  as  the  presence  of 
injurious  matter  or  the  lack  of  cultivation  or  food. 
For  the  production  of  legumes,  inoculation  of  the  soil  is 
often  beneficial.  The  commercial  production  and  dis- 
tribution of  the  organisms  forming  the  nodules  on  the 
roots  of  clover  and  other  leguminous  crops,  and  which 
cause  fixation  of  atmospheric  nitrogen,  was  first  pro- 
posed and  inaugurated  by  Nobbe.94  The  method  of  in- 
oculation consists  in  firct  multiplying  the  organisms 
in  nutritive  substances,  and  then  sprinkling  seeds  with 
the  diluted  solution.  Inoculation  with  soil  from  a  field 
where  clover  or  lupines  have  previously  been  grown  has 
also  been  successful,  particularly  in  reclaiming  sandy 
waste  lands  where  mineral  fertilizers  containing  potash 
and  phosphates  are  used  to  furnish  these  elements, 
while  the  more  expensive  nitrogen  is  acquired  indirectly 
from  the  air  through  the  clover.  Soils  in  a  high  state 
of  productiveness  are  not  usually  in  need  of  inoculation 
as  they  already  contain  all  the  essential  soil  organisms. 
Moore's  method  of  distributing  the  nitrogen-fixing  organ- 
isms of  legumes  in  the  form  of  cotton  cultures  has  been 
investigated  by  a  number  of  experiment  stations  and 
found  inefficient.87 

161.    Loss  of  Nitrogen  by  Fallowing   Rich  Lands. — 
Summer  fallowing  creates  conditions  favorable  to  nitri- 


NITROGEN,   NITRIFICATION,   NITROGENOUS   MANURES      145 

fication.  A  fallow  is  beneficial  to  a  succeeding  crop 
because  of  the  nitrogen  which  is  rendered  available. 
If  a  soil  is  rich  in  nitrogen  and  lime,  summer  fallow- 
ing causes  the  production  of  more  nitrates  than  can  be 
retained  in  the  soil.  The  crop  utilizes  only  a  part  of 
the  nitrogen  rendered  available,  the  rest  being  lost  by 
drainage,  ammonification,  and  denitrification.  Hence 
the  available  nitrogen  is  increased  while  the  total  nitro- 
gen is  greatly  decreased.9 


SOIL  BEFORE 
FALLOWING 

SOIL  AFTER 
FALLOWING 

Total  nitrogen  . 

0.154 
O.OO2 

0.142 
O.OO4 

The  gain  of  0.002  per  cent  of  soluble  nitrogen  was 
accompanied  by  a  loss  of  0.012  per  cent  of  total  nitro- 
gen. For  every  pound  of  available  nitrogen  there  was 
a  loss  of  six  pounds.  Bare  fallowing  of  land  for  an 
entire  year  should  not  be  practiced,  except  occasionally 
to  destroy  weeds  or  insects,  as  it  results  in  permanent 
injury  to  the  soil.  A  short  period  of  fallow  and  the 
practice  of  green  manuring  with  leguminous  crops  both 
enrich  the  soil  with  humus  and  nitrogen,  and  improve 
the  physical  properties. 

162.   Influence  of  Plowing  upon  Nitrification.  —  In  a 
rich  soil  containing  the  necessary  alkaline  matter,  nitrifi- 
cation goes  on  very  rapidly.     This  is  one  reason  why 
L 


146  SOILS  AND   FERTILIZERS 

shallow  plowing  on  new  breaking  gives  better  results 
than  deep  plowing.  Deep  plowing  at  first  causes  nitri- 
fication to  take  place  to  such  an  extent  that  the  crop  is 
over-stimulated  in  growth,  due  to  an  excess  of  available 
nitrogen.  Deep  plowing  and  thorough  cultivation  aid 
nitrification.  The  longer  a  soil  has  been  cultivated,  the 
deeper  and  more  thorough  must  be  the  cultivation. 

Early  fall  plowing  leaves  more  available  nitrogen  at 
the  disposal  of  the  crop  than  late  fall  plowing.  Nitrifi- 
cation takes  place  only  near  the  surface.  Hence  when 
late  spring  plowing  is  practiced  there  is  brought  to  the 
surface  raw  nitrogen,  while  the  more  active  nitrogen  has 
been  plowed  under,  and  is  beyond  the  reach  of  the  young 
plants  when  they  require  the  most  help  in  obtaining  food. 
The  various  methods  of  cultivation,  as  deep  and  shallow 
plowing,  spring  and  fall  plowing,  and  surface  cultivation, 
have  as  much  influence  upon  the  available  nitrogen 
supply  of  crops  as  upon  the  water  supply.  The  saying 
that  cultivation  makes  plant  food  available  is  particu- 
larly true  of  the  element  nitrogen,  the  supply  of  which 
is  capable  of  being  increased  or  decreased  to  a  greater 
extent  than  that  of  any  other  element. 

NITROGENOUS   MANURES 

163.  Sources  of  Nitrogenous  Manures.  —  The  materials 
used  for  enriching  soils  with  nitrogen,  to  promote  crop 
growth,  may  be  divided  into  two  classes:  (i)  organic 
nitrogenous  manures,  (2)  mineral  nitrogenous  manures. 


NITROGEN,   NITRIFICATION,    NITROGENOUS   MANURES      147 

Each  of  these  classes  has  a  different  value  as  plant 
food,  and  in  fact  there  are  marked  differences  in  fertili- 
zer value  between  materials  belonging  to  the  same  class. 
The  nitrogenous  organic  materials  used  for  fertilizing 
purposes  are :  dried  blood,  tankage,  meat  scraps  and 
flesh  meal,  fish  offal,  cottonseed  meal,  and  leguminous/ 
crops,  as  clover  and  peas.  The  nitrogen  in  these  sub- 
stances is  principally  in  the  form  of  protein.  When 
peat  and  muck  are  properly  used  they  also  may  be 
classed  among  the  nitrogenous  manures.  The  mineral 
nitrogenous  manures  are  nitrates,  as  sodium  nitrate,  and 
ammonium  salts,  as  ammonium  sulphate. 

164.  Dried  Blood.  —  This  is  obtained  by  drying  the 
blood  and  debris  from  slaughterhouses.  Frequently 
small  amounts  of  salt  and  slaked  lime  are  mixed  with 
the  blood.  It  is  richest  in  nitrogen  of  any  of  the 
organic  manures.  When  thoroughly  dry  it  may  contain 
14  per  cent  of  nitrogen.  As  usually  sold,  it  contains 
from  10  to  20  per  cent  of  water,  and  has  a  nitrogen 
content  of  from  9  to  13.  Dried  blood  contains  only 
small  amounts  of  other  fertilizer  elements ;  it  is  strictly 
a  nitrogenous  fertilizer,  readily  yielding  to  the  action  of 
micro-organisms  and  to  nitrification.  On  account  of  its 
fermentable  nature,  it  is  a  quick-acting  fertilizer,  and  is 
one  of  the  most  valuable  of  the  organic  materials  used  as 
manure.  It  gives  the  best  returns  on  an  impoverished 
soil  to  aid  crops  in  the  early  stages  of  growth,  before 
the  inert  nitrogen  of  the  soil  becomes  available.  Dried 


148  SOILS    AND   FERTILIZERS 

blood  may  be  applied  as  a  top  dressing  on  grass  land, 
and  it  is  also  an  excellent  form  of  fertilizer  for  many 
garden  crops ;  but  it  should  not  be  placed  in  direct  con- 
tact with  seeds,  as  it  will  cause  rotting,  nor  should  it  be 
used  in  too  large  amounts.  Three  hundred  pounds  per 
acre  is  as  much  as  should  be  applied  at  one  time.  When 
too  much  is  used  losses  of  nitrogen  may  occur  by  leach- 
ing and  by  denitrification.  It  is  best  applied  directly  to 
the  soil  as  a  top  dressing  in  the  case  of  grass,  or  near 
the  seeds  of  garden  crops,  and  not  mixed  with  unslaked 
lime  or  wood  ashes,  but  each  should  be  used  separately. 
As  all  plants  take  up  their  nitrogen  in  the  early  stages 
of  growth,  nitrogenous  fertilizers  as  blood  should  be  ap- 
plied before  seeding  or  soon  after.  An  application  of 
dried  blood  to  partially  matured  garden  crops  will  cause 
a  prolonged  growth  and  very  late  maturity. 

Storer  gives  the  following  directions  for  preserving 
any  dried  blood  produced  upon  farms.22  "  The  blood 
is  thoroughly  mixed  in  a  shallow  box  with  4  or  5  times 
its  weight  of  slaked  lime.  The  mixture  is  covered  with 
a  thin  layer  of  lime  and  left  to  dry  out.  It  will  keep  if 
stored  in  a  cool  place,  and  may  be  applied  directly  to 
the  land  or  added  to  a  compost  heap." 

The  price  per  pound  of  nitrogen  in  the  form  of  dried 
blood  can  be  determined  from  the  cost  and  the  analysis 
of  the  material.  A  sample  containing  9  per  cent  of  nitro- 
gen and  selling  for  $28  per  ton  is  equivalent  to  15.55 
cents  per  pound  for  the  nitrogen  (2000x0.09=180. 
5.oo-f-  1 80  =  15.55  cents). 


NITROGEN,    NITRIFICATION,    NITROGENOUS    MANURES      149 


165.  Tankage  is  composed  of  refuse  matter,  as  bones, 
trimmings  of  hides,  hair,  horns,  hoofs,  and  some  blood. 
The  fat  and  gelatin  are,  as  a  rule,  first  removed  by  sub- 
jecting the  material  to  superheated  steam.  This  mis- 
cellaneous refuse,  after  drying,  is  ground  and  some- 
times mixed  with  a  little  slaked  lime  to  prevent  rapid 
fermentation. 

Tankage  contains  less  nitrogen  but  more  phosphoric 
acid  than  dried  blood.  Owing  to  its  miscellaneous  na- 
ture, it  is  quite  variable  in  composition,  as  the  following 
analyses  of  tankage  from  the  same  abattoir  at  different 
times  show : 14 


FIRST 
YEAR 

SECOND 
YEAR 

THIRD 
YEAR 

Moisture 
Nitrogen 
Phosphoric 

per  cent      

10-5 

5-7 

12.2 

9.8 

7-6 
10.6 

10.9 
6.4 
II.7 

u 

acid    "       

As  a  general  rule,  tankage  contains  from  5  to  8  per 
cent  of  nitrogen  and  from  5  to  12  per  cent  of  phos- 
phoric acid.  It  is  much  slower  in  its  action  than  dried 
blood,  and  supplies  the  crop  with  both  nitrogen  and 
phosphoric  acid.  Tankage  is  a  valuable  form  of  fer- 
tilizer for  garden  purposes.  It  may  also  be  used  as 
a  top  dressing  on  grass  lands,  or  spread  broadcast  on 
grain  lands.  It  is  best  to  apply  the  tankage,  when  pos- 
sible, a  few  days  prior  to  seeding,  and  it  should  not 
come  in  contact  with  seeds.  Two  hundred  and  fifty 


I5O  SOILS    AND     FERTILIZERS 

pounds  per  acre  is  a  safe  dressing,  and  when  there  is 
sufficient  rain  to  ferment  the  tankage,  400  pounds  per 
acre  may  be  used.  A  dressing  of  800  pounds  in  a  dry 
season  would  be  destructive  to  vegetation.  On  impov- 
erished soil  more  may  be  used  than  on  soils  which  are 
for  various  reasons  out  of  condition.  The  cost  of  the 
nitrogen  as  tankage  is  determined  from  the  composi- 
tion and  selling  price.  If  tankage  containing  7  per 
cent  of  nitrogen  and  12  per  cent  of  phosphoric  acid  is 
selling  for  $32  per  ton,  what  is  the  cost  of  the  nitrogen 
per  pound  ?  The  market  value  of  phosphoric  acid,  in 
the  form  of  bones,  should  first  be  ascertained.  Sup- 
pose bone  phosphoric  acid  is  selling  for  4  cents  per 
pound.  The  phosphoric  acid  in  the  ton  of  tankage 
would  then  be  worth  $9.60,  making  the  nitrogen  cost 
$22.40.  The  140  pounds  of  nitrogen  in  the  ton  of  fer- 
tilizer would  be  worth  $22.40,  or  16  cents  per  pound. 
In  eastern  markets  the  price  of  tankage  is  usually  higher 
than  near  the  large  packing  houses  of  the  West. 

166.  Flesh  Meal.  —  The  flesh  refuse  from  slaughter- 
houses is  sometimes  kept  separate  from  the  tankage 
and  sold  as  flesh  meal,  the  fat  and  gelatin  being  first 
removed  and  used  for  the  manufacture  of  glue  and 
soap.  Flesh  meal  is  variable  in  composition  and  may 
be  very  slow  in  decomposing.  It  contains  from  4  to  8 
per  cent  or  more  of  nitrogen,  with  an  appreciable  amount 
of  phosphoric  acid.  Occasionally  it  is  used  for  feeding 
poultry  and  hogs,  and  cattle  to  a  limited  extent.  The 


NITROGEN,    NITRIFICATION,    NITROGENOUS    MANURES       1$! 

fertilizer  value  of  the  dung  is  nearly  equivalent  to  the 
original  value  of  the  meal. 

167.  Fish  Scrap. — The  flesh  of  fish  is  very  rich  in 
nitrogen.49     The  offal  parts,  as  heads,  fins,  tails,  and  intes- 
tines, are  dried  and  prepared  as  a  fertilizer.    Some  species 
of  fish  which  are  not  edible  are  caught  in  large  numbers 
to  be  used  for  this  purpose.     In  seacoast  regions,  fish  fer- 
tilizer is  one  of  the  cheapest  and  best  of  the  nitrogenous 
manures.     It  is  richer  in  nitrogen  than  tankage  or  flesh 
meal,  and  in  many  cases  equal  to  dried  blood.     It  read- 
ily undergoes  nitrification  and  is  a  quick-acting  fertilizer. 

168.  Seed  Residues. —  Many  seeds,  as  cottonseed  and 
flaxseed,  are  exceedingly  rich  in  nitrogen.    When  the  oil 
has  been  removed,  the  flaxseed  and  cottonseed  cake  are 
proportionally  richer  in  nitrogen  than  the  original  seed. 
This  cake  is  usually  sold  for  cattle  food,  but  occasionally 
is  used  as  fertilizer.     It  contains  from  6  to  7  per  cent  of 
nitrogen,  and  compares  fairly  well  in  nitrogen  content 
with  animal  bodies.     Cottonseed  cake  and  meal  are  not 
so  quick  acting  as  dried  blood,  but  when  used  in  south- 
ern latitudes  a  little  time  before  seeding,  the  nitrogen 
becomes   available   for  crop  purposes.     Oil   meals,  as 
cottonseed  and  linseed,  containing  a  high  per  cent  of 
oil,  are  much  slower  in  decomposing  than  those  which 
contain  but  little  oil.     It  is  better  economy  to  feed  the 
cake  to  stock  and  use  the  manure  than  to  apply  the  cake 
directly  to  the  land.     Occasionally,  however,  cottonseed 


152  SOILS    AND    FERTILIZERS 

meal  has  been  so  low  in  price  that  its  use  as  a  fertilizer 
has  been  admissible. 

A  ton  of  cottonseed  meal,  costing  $20  and  containing 
2  per  cent  of  phosphoric  acid  and  7  per  cent  of  nitro- 
gen, would  be  equivalent  to  13.1  cents  per  pound  for 
the  nitrogen,  which  is  frequently  cheaper  than  purchas- 
ing some  other  nitrogenous  fertilizer. 

169.  Leather,  Wool  Waste,  and  Hair  are  rich  in  nitro- 
gen, but  on  account  of  their  slowness  in  decomposing 
are  unsuitable  for  fertilizer  purposes.     When  present  in 
fertilizers  they  give  poor  field  results. 

170.  Available  Nitrogen.  —  One  of  the  methods  em- 
ployed to  detect,  in  fertilizers,  the  presence  of   inert 
forms  of  nitrogen,  as  leather,  is  to  digest  the  material  in 
prepared  pepsin  solution.50     Substances  like  dried  blood 
are  nearly  all  soluble  in  the  pepsin,  while  leather  and  other 
inert  forms  are  only  partially  so.     The  solubility  of  the 
organic  nitrogen  in  pepsin  solution  determines,  to  a  great 
extent,  the  value  of  the  material  as  a  fertilizer.61 


PER  CENT  OF  NITROGEN 
SOLUBLE  IN  PREPARED 
PEPSIN  SOLUTION 

04.  2 

86.4 

71.7 

Tankajje    

71.6 

Hoof  and  horn  meal   

1O.O 

Leather      

16.7 

NITROGEN,    NITRIFICATION,    NITROGENOUS    MANURES       153 

Some  of  the  organic  forms  of  nitrogen  readily  undergo 
nitrification  and  become  available  as  plant  food,  while 
other  forms  are  inactive.  Vegetation  tests  show  that 
from  60  to  75  per  cent  of  the  nitrogen  of  dried  blood, 
tankage,  cottonseed  meal,  and  fish  meal  are  available  as 
plant  food  the  year  they  are.  used  as  fertilizer.  The 
available  nitrogen  of  fertilizers  includes  nitrates  and 
ammonium  salts  and  such  forms  of  organic  matter  as 
readily  undergo  nitrification.  Potassium  permanganate 
with  and  without  sodium  hydroxide  is  also  employed 
as  a  solvent  for  available  nitrogen.52 

171.  Peat  and  Muck.  —  Peat  and  muck  are  rich  in 
nitrogen  which  is  in  an  insoluble  form  and  is  with  diffi- 
culty nitrified.  When  mixed  with  lime  and  stable 
manure,  particularly  liquid  manure,  fermentation  is 
induced  and  a  valuable  manure  produced.  Muck  and 
peat  should  be  dried  and  sun-cured,  and  then  used  as 
absorbents  in  stables.  Peat  differs  from  muck  in  being 
fibrous.  If  the  muck  is  acid,  lime  (not  quicklime)  should 
be  used  with  it  in  the  stable,  as  directed  under  farm 
manures.  When  easily  obtained,  muck  is  one  of  the 
cheapest  forms  of  nitrogen. 

COMPOSITION  OF  DRY  MUCK  SAMPLES9 


NITROGEN 
PER  CENT 

Marshy  place,  producing  hay      

2  21 

Marshy  place,  dry  in  late  summer  

2  OI 

Old  lake  bottom  

i  81 

154  SOILS   AND    FERTILIZERS 

172.  Leguminous   Crops   as   Nitrogenous  Manures  — 
The  frequent  use  of  leguminous  crops  for  manurial  pur- 
poses is  the  cheapest  way  of  obtaining  nitrogen.     When 
the  crop  is  not  removed  from  the  land  but  is  plowed 
under  while  green,  the  practice  is  called  green  manur- 
ing.    This  does  not  enrich  the  land  with  any  mineral 
material,  but  results   in   changing   inert  plant  food   to 
humate  forms.     Green  manuring  with  leguminous  crops 
should  take  the  place  of  bare  fallow,  as  its  effects  upon 
the  soil  are   more  beneficial.     With   green   manuring, 
nitrogen  is  added  to  the  soil,  while  with  bare  fallow  there 
is  a  loss  of  nitrogen.     Leguminous  crops,  as  clover,  peas, 
crimson  clover,  and  cowpeas,  should  be  made  to  serve 
as  the  main  source  of  the  nitrogen  for  crop  production. 
A  good  crop  of  clover  will  return  to  the  soil  over  200 
pounds  of  nitrogen  per  acre. 

173.  Sodium    Nitrate.  —  The    nitric    nitrogen    most 
frequently  met   with   in   commercial   forms   is   sodium 
nitrate,    commonly  known   as   Chili  saltpeter.     It  is  a 
natural  deposit  found   extensively   in  Chili,  Peru,  and 
the  United  States  of  Colombia.     Various  theories  have 
been  proposed  to  account  for  these  deposits,  but  it  is 
difficult  to  determine  just  how  they  have  been  formed.10 
The  commercial  value  of  nitrogen  in  fertilizers  is  regu- 
lated mainly  by  the  price  of  sodium  nitrate,  which,  when 
pure,    contains    16.49  Per  cent  of   nitrogen.     Commer- 
cial  sodium   nitrate  is   from   95  to  97  per  cent  pure. 
An  ordinary   sample   contains   about    16   per   cent  of 


NITROGEN,    NITRIFICATION,    NITROGENOUS    MANURES       155 

nitrogen  and  costs  from  $50  to  $60  per  ton,  making 
the  nitrogen  worth  from  15  to  18  cents  per  pound. 
Sodium  nitrate  is  the  most  active  of  all  the  nitrogenous 
manures.  It  is  soluble  and  does  not  have  to  undergo 
the  nitrification  process  before  being  utilized  by  crops. 
On  account  of  its  extreme  solubility  it  should  be  ap- 
plied sparingly,  for  it  cannot  be  retained  in  the  soil. 
As  a  top  dressing  on  grass,  it  will  respond  by  impart- 
ing a  rich  green  color.  It  may  be  used  at  the  rate  of 
250  pounds  per  acre,  but  a  much  lighter  application  will 
generally  be  found  more  economical.  Sodium  nitrate 
should  not  be  used  when  heavy  dressings  of  farm 
manure  are  applied,  as  denitrifi cation  may  result  from 
such  a  practice.  In  small  amounts  it  is  the  fertilizer 
most  frequently  resorted  to  when  the  forcing  of  crops 
is  desired,  as  in  early  market  gardening.  Its  use  for 
fertilizing  horticultural  crops  has  become  equally  as  ex- 
tensive as  for  general  farm  crops.  Excessive  amounts, 
however,  may  produce  injurious  results.  Sodium  nitrate 
•stimulates  a  rank  growth  of  dark  green  foliage  and 
retards  the  maturity  of  plants,  but  when  properly  used 
is  one  of  the  most  valuable  of  the  nitrogenous  ferti- 
lizers. 

174.  Ammonium  Sulphate.  —  Ammonium  sulphate  is 
obtained  as  a  by  product  in  the  manufacture  of  illu- 
minating gas  and  is  extensively  sold  as  a  fertilizer.  It 
usually  contains  about  20  per  cent  of  nitrogen,  equiv- 
alent to  95  per  cent  of  ammonium  sulphate,  the  re- 


156  SOILS   AND   FERTILIZERS 

maining  5  per  cent  being  moisture  and  impurities. 
Ammonium  sulphate  is  not  generally  considered  the 
equivalent  of  sodium  nitrate,  as  it  is  believed  it  must 
undergo  nitrification  before  being  utilized  as  plant 
food.  It  is,  however,  a  valuable  form  of  nitrogen.  Ex- 
periments show  that  plants  may  utilize  ammonia  directly 
without  nitrification  processes  first  taking  place.68  The 
statements  regarding  the  use  of  sodium  nitrate  apply 
equally  well  to  the  use  of  ammonium  sulphate.  Am- 
monium chloride  and  ammonium  carbonate  are  not 
suitable  for  fertilizers  on  account  of  their  destructive 
action  upon  vegetation. 

175.  Calcium  Nitrate  and  Cyanamid,  Ca(NO3)2  and 
CaCN2.  —  The  nitrogen  of  these  compounds  is  obtained 
from  the  free  nitrogen  of  the  air  by  electrical  processes. 
Calcium  nitrate  is  made  by  treating  lime  with  nitric  acid 
resulting  from  the  oxides  of  nitrogen  produced  in  the 
air  by  electrical  action.  It  is  a  valuable  form  of  nitrogen 
fertilizer.  Calcium  cyanamid  is  made  by  heating  together 
coal  and  lime  in  an  electrical  furnace  through  which  a 
current  of  nitrogen  gas,  obtained  from  the  air,  is  passed. 
Experiments  with  calcium  cyanamid  as  a  fertilizer  show 
that  the  nitrogen  undergoes  nitrification  and  becomes 
available  as  plant  food.68  It  is  claimed  that  these  com- 
pounds of  nitrogen  Ca(NO3)2  and  CaCN2,  in  which  the 
nitrogen  is  obtained  from  the  air,  will  eventually  be  pro- 
duced at  such  a  low  cost  as  to  permit  their  extensive  use 
as-fertilizers. 


NITROGEN,    NITRIFICATION,    NITROGENOUS    MANURES 

176.  Nitrogen  and  Ammonia  Equivalent  of  Fertilizers. 

—  Nitrogenous  fertilizers  are  sometimes  represented 
as  containing  a  certain  amount  of  ammonia  instead  of 
nitrogen.  Fourteen-seventeenths  of  ammonia  is  nitro- 
gen, and  if  a  fertilizer  contains  2.25  per  cent  ammonia, 
it  is  equivalent  to  1.85  per  cent  of  nitrogen.  To  convert 
NH3  results  to  an  N  basis,  multiply  by  0.823. 

177.  Purchasing  Nitrogenous  Manures.  —  In  purchas- 
ing a  nitrogenous  manure,  the  special  purpose  for  which 
it  is  to  be  used  should  always  be  considered.     Under 
some  conditions,  as  forcing  a  crop  on  an   impoverished 
soil,  sodium  nitrate  is  desirable.     Under  other  conditions, 
tankage,  cottonseed  cake,  or  some  other  form  of  nitro- 
gen may  be  better.     There  is  annually  expended  in  pur- 
chasing nitrogenous  fertilizers  a  large  amount  of  money 
which   could   be   expended   more   economically   if   the 
science  of  fertilizing  were  given  a  more  careful  study, 
and  if  a  larger  share  of  the   nitrogen   for  crop  pur- 
poses were  obtained  indirectly  from  the  air  through  the 
agency  of  legumes.     The  uses  of  nitrogenous  fertilizers 
for  special  crops  and  the  testing  of  soils  to  determine 
any  deficiency  in  nitrogen  are  discussed  in  Chapters 
X  and  XI,  which  treat  of  commercial  fertilizers  and  the 
food  requirements  of  farm  crops. 


CHAPTER  V 

FARM  MANURES 

178.  Variable  Composition  of  Farm  Manures.  —  The 

term  '  farm  manure '  does  not  designate  a  product  of 
definite  composition.  Manure  is  the  most  variable  in 
chemical  composition  of  any  of  the  materials  produced 
on  the  farm.  It  may  contain  a  large  amount  of  straw, 
in  which  case  it  is  called  coarse  manure ;  or  it  may  con- 
tain only  the  solid  excrements  and  a  little  straw,  the 
liquid  excrements  being  lost  by  leaching ;  then  again 
it  may  consist  of  the  droppings  of  poorly  fed  animals, 
or  of  the  mixed  excrements  of  different  classes  of  well- 
fed  animals. 

The  term  '  stable  manure '  has  been  proposed  for  that 
product  which  contains  all  of  the  solid  and  liquid  excre- 
ments with  the  necessary  absorbent,  before  any  losses 
have  been  sustained.16  The  term  'barnyard  manure'  is 
restricted  to  that  which  accumulates  around  some  barns 
and  farmyards,  and  is  exposed  to  leaching  rains  and  the 
drying  action  of  the  sun. 

179.  Average  Composition  of  Manures.  —  The  solid 
excrements  of  animals  contain  from  60  to  85  per  cent 
of  water;  when  mixed  with  straw,  and  the  liquid  ex- 
crements   are   retained,    the    mixed   manure   contains 

158 


FARM    MANURES 


159 


about  75  per  cent  of  water.  The  nitrogen  varies  from 
0.4  to  0.9  per  cent,  according  to  the  nature  of  the  food 
and  the  extent  to  which  other  factors  have  affected  the 
composition.  In  general,  animals  consuming  liberal 


2*3. 

FiG.  34.    Average  Composition  of  Fresh 

Manure. 

i.  Nitrogen.        2.  Phosphoric  acid. 
3.  Potash.  4.  Mineral  matter. 


42.131 

FiG.  35.     Manure  after  Six 
Months'  Exposure. 


amounts  of  coarse  fodders  produce  manure  with  a 
higher  per  cent  of  potash  than  of  phosphoric  acid. 
This  is  because  the  potash  in  the  food  exceeds  the 
phosphoric  acid.  Farm  manures  also  contain  lime, 
magnesia,  and  other  minerals  present  in  plants  and 
designated  as  essential  ash  elements.  The  average 
composition  of  mixed  stable  manure  is  as  follows : 


AVERAGE 
PER  CENT 

RANGE 
PER  CENT 

Nitrogen,  N     

o.co 

0.4  to  0.8 

Phosphoric  acid,  P2O5   

o.ic 

O.2  to  O.C 

Potash,  K2O    

o.co 

O."l  to  O.Q 

i6o 


SOILS   AND    FERTILIZERS 


In  calculating  the  amount  of  fertility  in  manures,  it 
is  more  accurate  to  compute  the  value  from  the  food 
consumed  and  the  conditions  under  which  the  manure 
has  been  produced,  than  to  use  figures  expressing  aver- 
age composition. 

180.  Factors   which   influence    the   Composition   and 
Value  of  Farm  Manure. — 

I.    Kind  and  amount  of  absorbents  used. 
II.    Kind  and  amount  of  food  consumed. 

III.  Age  and  kind  of  animals. 

IV.  Methods  employed  in  collecting,  preserving,  and 
utilizing  the  manure. 

Any  one  of  the  above,  as  well  as  many  minor  fac- 
tors, may  influence  the  composition  and  value  of  farm 
manures. 

181.  Absorbents.  —  The  absorbent  generally  used  is 
straw.     Wheat  straw  and  barley  straw  have  about  the 
same  manurial  value ;  oat  straw  is  more  valuable  than 
either.     The  average  composition  of  straw  and  other 
absorbents  is  as  follows  : 


STRAW 
PER  CENT 

LEAVES 
PER  CENT 

PEAT 
PER  CENT 

SAWDUST 
PER  CENT 

Nitrogen  t  >  ... 

0.40 
0.36 
0.80 

0.6 
o-3 
o-3 

1.0 

O.I 
0.2 
0.4 

Phosphoric  acid  .  ... 
Potash  

When  a  large  amount  of  straw  is  used  the  percentage 
amounts  of  nitrogen  and  phosphoric  acid  are  decreased. 


FARM    MANURES  l6l 

while  the  per  cent  of  potash  is  slightly  increased.  Saw- 
dust and  loam  both  make  the  manure  more  dilute.  Dry 
peat  makes  the  manure  richer  in  nitrogen.  The  ab- 
sorptive power  of  these  different  materials  is  about  as 
follows : 14 


PER  CENT  OF 
WATER  ABSORBED 

Fine  cut  straw       

7O.O 

Coarse  uncut  straw    

18.0 

Peat    

60.0 

Sawdust  

A  C.O 

The  proportion  of  absorbents  in  manure  ranges  from 
a  fifth  to  a  third  of  the  total  weight  of  the  manure. 

182.  Use  of  Peat  and  Muck  as  Absorbents.  —  Because 
of  the  high  content  of  nitrogen  in  peat  and  the  power 
which  it  possesses  when  dry  of  absorbing  water,  it  is 
a  valuable  material  to  use  as  an  absorbent  in  stables. 
As  previously  stated,  peat  is  slow  to  decompose,  but 
when  mixed  with  the  liquid  manure  it  readily  yields  to 
fermentation,  particularly  if  a  little  land  plaster  or  marl 
be  used  in  the  stable  along  with  the  peat.  Peat  has 
high  absorptive  power  for  gases  as  well  as  for  liquids, 
and  when  used  the  sanitary  condition  of  stables  is  im- 
proved and  the  air  is  rendered  particularly  free  from 
foul  odors. 


162 


SOILS    AND    FERTILIZERS 


RELATION  OF  FOOD  CONSUMED  TO  MANURE  PRODUCED 

183.  Bulky  and  Concentrated  Foods.  —  The  more  con- 
centrated and  digestible  the  food  consumed,  the  more 
valuable  is  the  manure.  Coarse  bulky  fodders  always 
give  a  large  amount  of  a  poor  quality  of  manure.  For 
example,  the  manure  from  animals  fed  on  timothy  hay 
and  that  from  animals  fed  on  clover  hay  and  grain 
show  a  wide  difference  in  composition.  The  dry  matter 
of  timothy  hay  is  about  55  per  cent  digestible.  From 
a  ton  of  timothy  hay  there  is  about  790  pounds  of  dry 
matter  in  the  manure.  The  nitrogen,  phosphoric  acid, 
and  potash  in  the  food  consumed  are  nearly  all  returned 
in  the  manure,  except  under  those  conditions  which  will 
be  noted.  The  manure  from  a  ton  of  mixed  feed,  as 
clover  and  bran,  is  smaller  in  amount  but  more  concen- 
trated than  that  produced  from  timothy.  In  a  ton  of 
timothy  and  in  a  ton  of  mixed  feed  (1500  Ibs.  clover, 
500  Ibs.  bran)  there  are  present: 


TIMOTHY 
LBS. 

MIXED  FEED 
LBS. 

Nitrogen     

2C.O 

A.O  O 

Phosphoric  acid  

Q.O 

2A.O 

Potash  

4.O.O 

30  o 

The  nitrogen,  phosphoric  acid,  and  potash  of  these 
two  rations  are  retained  in  the  animal  body  in  dissimi- 
lar amounts,  10  per  cent  more  of  these  elements  being 


FARM    MANURES  163 

retained  from  the  more  liberal  ration,  due  to  more 
favorable  conditions  for  growth.  Because  of  this  fact 
there  is  present  in  the  manure  from  the  mixed  feed  one 
half  more  nitrogen,  and  two  and  one  half  times  as  much 
phosphoric  acid,  as  in  the  manure  from  the  timothy 
hay,  which,  free  from  bedding,  contains  about  790 
pounds  of  indigestible  matter,  while  the  manure  from 
the  mixed  feed  contains  760  pounds,  the  mixed  ration 
being  more  digestible.  If  both  manures  contain  the 
same  amount  of  absorbents,  the  manure  from  the  ton 
of  mixed  clover  and  bran  will  weigh  slightly  less, 
but  contain  more  fertility  than  that  from  the  timothy 
hay. 

The  value  of  manure  can  be  accurately  determined 
from  the  composition  of  the  food  consumed  and  the 
care  which  the  manure  has  received.  Only  a  small 
amount  of  the  nitrogen  in  the  food  is  permanently 
retained  in  the  body.  The  larger  portion  is  used  for 
repair  purposes,  the  nitrogen  of  the  tissues  which 
have  been  renewed  being  voided  as  urea  in  the 
liquid  excrements.  Some  of  the  nitrogenous  com- 
pounds of  the  food  are  utilized  for  the  production 
of  fat,  in  which  case  the  nitrogen  is  voided  in  the 
excrements.  The  fact  that  but  little  of  the  nitrogen 
and  mineral  matter  of  the  food,  under  most  condi- 
tions, is  retained  in  the  body  is  shown  by  the  in- 
vestigations of  Lawes  and  Gilbert  upon  the  compo- 
sition of  the  flesh  added  to  animals  while  undergoing 
the  fattening  process.56 


164 


SOILS   AND    FERTILIZERS 


INCREASE  DURING  FATTENING 


WATER 

DRY 
MATTER 

FAT 

NITROGENOUS 
MATTER 

ASH 

Ox  

24  6 

7C  A 

66  2 

7  60 

T    At 

fy-4 

/.uy 

1.47 

Sheep  .... 

20.1 

79-9 

70.4 

7-13 

2.36 

Pig      .... 

22.  0 

78.0 

71-5 

6.44 

O.O6 

The  results  of  numerous  digestion  experiments  show 
that  when  the  food  undergoes  digestion  only  from  5 
to  15  per  cent  of  the  nitrogen  is,  as  a  rule,  retained 
in  the  body.  The  nitrogen  of  the  food  is  utilized 
largely  to  replace  that  which  has  been  required  for 
vital  functions ;  it  enters  the  body,  undergoes  digestion 
changes,  is  utilized  for  some  vital  function,  and  is  then 
voided  in  the  excrements. 

The  digestion  of  food  has  been  compared  to  the 
combustion  of  fuel :  the  undigested  products  of  the 
solid  excrements  represent  the  ashes,  and  the  urine 
represents  the  volatile  products.  When  wood  is  burned 
the  nitrogen  is  converted  into  volatile  products.  When 
food  is  digested  and  utilized  by  the  body  the  digestible 
nitrogen  is  mainly  converted  into  urea,  while  the  indi- 
gestible nitrogen  is  voided  in  the  dung.  In  the  solid 
and  liquid  excrements  of  animals  from  80  to  95  per 
cent  of  the  nitrogen,  phosphoric  acid,  and  potash  of  the 
food  consumed  is  present. 

184.  Comparative  Composition  of  Solid  and  Liquid  Ex- 
crements. —  In  composition  the  liquid  excrements  differ 


FARM    MANURES 


i65 


from  the   solids  in  having  a  much  larger  amount  of 
nitrogen  and  less  phosphoric  acid.66 


WATER 

NITROGEN 

PHOSPHORIC  ACID 

POTASH 

c 
.88 

^S 
cn& 

M    C 

."2  J} 

tr  J; 

"1 

"O 

—  - 

li 

CT»- 

c 

fl 

°*  Jj 

c 
jl 

Si 

-- 

BBft 

JO, 

fficE 

3d, 

Cows  .     . 

76 

89.0 

O.5O 

1.  2O 

o-35 



0.30 

Horses     . 

84 

92.0 

O.JO 

0.86 

0.25 



O.IO 

Pigs    .     . 

80 

97.0 

O.60 

0.80 

0.45 

O.I2 

0.50 

Sheep 

58 

86.5 

0.75 

1.40 

0.60 

0.05 

0.30 

The  nitrogen  in  the  food  consumed  influences  the 
amount  of  water  in  the  manure.  As  a  rule,  a  highly 
concentrated  nitrogenous  ration  produces  a  higher  per 
cent  of  water  than  a  well-balanced  ration.  There  is 
but  little  phosphoric  acid  in  the  liquid  excrements  of 
horses  and  cows,  while  that  of  sheep  and  swine  contains 
appreciable  amounts. 

The  liquid  manure  is  more  constant  both  in  compo- 
sition and  amount  than  the  solid  excrements.  This 
fact  may  be  observed  from  the  following  table,  which 
gives  the  composition  of  the  solid  and  liquid  excre- 
ments of  hogs  when  fed  on  different  amounts  of 
grain.57 

The  nitrogenous  waste  matter  in  the  urine  is  nearly 
the  same  whether  an  animal  be  gaining  or  losing  in  flesh, 
and  hence  it  is,  the  urine  is  more  constant  in  composi- 
tion and  quantity  than  the  solid  excrements. 


i66 


SOILS    AND    FERTILIZERS 


LBS. 

KIND  OF  FOOD  DAILY 

SOLID 
EXCREMENTS 

LIQUID 
EXCREMENTS 

H 

g 
o   • 
|jj 

1! 

o 

1  1 

OT3   n 

c  _. 
v  a 

o 

1  * 

1  8 

OT3  v. 

2(2 

to    «&< 

** 

C-  5  Ci 

6 

51 

61 

Barley  and  shorts  .... 
Barley      

8 

4 
2j 

If 

0.57 

°43 
0.80 
0.82 

0.72 
O.7O 

0.89 

2.05 
2.06 
2.65 
2.05 

O.O6 

0.16 

O.2O 

0.29 

Corn  and  shorts     .... 
Corn  

(In  each  experiment  the  amount  of  liquid  excrement  was  4  pounds.) 

The  amount  and  composition  of  the  solid  excre- 
ments vary  with  the  amount  and  kind  of  food  con- 
sumed. If  the  food  is  indigestible,  the  solid  excrements 
contain  a  larger  part  of  the  nitrogen  as  indigestible 
protein.  When  an  animal  is  supplied  with  the  proper 
food  for  all  purposes,  normal  conditions  exist,  and  the 
amount  of  nitrogen  voided  in  the  liquid  and  solid 
excrements  is  equal  to  that  supplied  in  the  food  con- 
sumed, except  in  the  case  of  growing  and  milk-pro- 
ducing animals. 

Experiments  at  the  Rothamsted  Station  show  that 
from  57  to  79  per  cent  of  the  total  nitrogen  in  the 
food  of  farm  animals  is  voided  in  the  liquid  excrements, 
and  from  16  to  22  per  cent  is  voided  in  the  solids. 
Nearly  all  of  the  mineral  elements  of  the  food  are 
voided  in  the  excrements,  less  than  4  per  cent  being 


FARM    MANURES 


retained  in  the  body ;  in  the  case  of  milk  cows  about  10 
per  cent  of  the  ash  of  the  food  is  recovered  in  the  milk. 

185.  Manurial  Value  of  Foods.  —  The  manurial  value 
of  a  fodder  is  determined  from  the  amount  and  com- 
mercial value  of  the  nitrogen,  phosphoric  acid,  and 
potash  present  in  the  fodder.  A  ton  of  clover  hay,  for 
example,  contains  35  pounds  of  nitrogen,  14  pounds  of 


NITROGEN 

N 
LBS. 


PHOSPHORIC  ACID 


LBS. 


POTASH 
K2O 
LBS. 


Timothy  hay 25 

Clover  hay 35 

Wheat  straw 1 1 

Oat  straw 12 

Wheat 45 

Oats 33 

Barley 40 

Rye 42 

Flax 87 

Corn 32 

Wheat  shorts 48 

Wheat  bran 54 

Linseed  meal 100 

Cottonseed  meal 130 

Milk 10 

Cheese 90 

Live  cattle 53 

Potatoes 7 

Butter I 

Live  pigs 40 


9 

14 

4 

4 

20 

16 

18 

20 

32 


52 

35 

35 

3 

23 
37 

3 
i 

17 


40 
3° 

12 

18 

12 
II 
II 
13 
H 

8 

20 

3° 

25 

56 

3 
5 
3 
ii 
i 
3 


168  SOILS    AND    FERTILIZERS 

phosphoric  acid,  and  30  pounds  of  potash.  When  the 
nitrogen  is  worth  16  cents  per  pound,  the  phosphoric 
acid  6  cents,  and  the  potash  5  cents,  the  clover  hay  has 
a  manurial  value  of  $7.94  per  ton.  Lawes  and  Gilbert 
estimate  that  80  per  cent  of  the  fertility  in  fodders  is, 
as  a  rule,  returned  in  the  manure. 

In  the  preceding  table  are  given  the  pounds  of  nitro- 
gen, phosphoric  acid,  and  potash  per  ton  of  some  farm 
products.68 

186.  Commercial  Value  of  Manures.  —  When  the  value 
of  farm  manure  is  calculated  on  the  same  basis  as  com- 
mercial fertilizers,  it  will  be  found  that  stable  manure 
is  worth  from  $2  to  $3.50  per  ton.  The  value  of  the 
increased  crops  resulting  from  its  use  varies  with  con- 
ditions. Farm  manures  favorably  influence  the  yield  of 
crops  for  a  number  of  years.  As  for  example,  a  dress- 
ing of  8  tons  of  manure  will  make  average  prairie  land 
yield  upwards  of  20  bushels  per  acre  more  corn  the 
first  year,  5  bushels  more  wheat  the  second  year,  and  8 
bushels  or  so  more  of  other  grains  the  third  year,  with 
slightly  increased  yields  in  subsequent  years,  all  due 
to  the  original  application  of  the  manure.  It  is  often 
necessary  to  apply  farm  manure  in  order  to  secure  a 
stand  of  clover,  which  enriches  the  soil  with  nitrogen.  It 
sometimes  takes  from  two  to  three  years  for  the  manure 
entirely  to  repay  the  cost  of  its  application.  Its  influence 
is  felt,  however,  for  a  much  longer  time.  In  calculating 
the  value  of  farm  manure,  the  returns  from  its  use  for  a 


FARM    MANURES  169 

number  of  years  must  be  considered  and  also  its  in- 
fluence in  permanently  increasing  the  value  of  the  land. 

It  is  sometimes  stated  that  the  phosphoric  acid  and 
potash  in  stable  manure  is  not  so  soluble  as  that  in 
commercial  fertilizers,  and  consequently  is  worth  less. 
While  not  so  soluble  in  the  form  of  manure,  it  fre- 
quently happens  that  the  phosphoric  acid  and  potash 
in  the  commercial  fertilizers  become,  through  fixation 
processes,  less  soluble  when  mixed  with  the  soil  than 
the  same  elements  in  stable  manure. 

Stable  manure  is  valuable  not  only  for  the  fertility  con- 
tained but  also  because  it  makes  the  inert  plant  food  of 
the  soil  more  available  and  exercises  such  a  favorable  in- 
fluence on  the  water  supply  of  crops  ;  hence  it  is  justi- 
fiable to  assign  the  same,  if  not  a  higher,  value  to  the 
elements  in  well-prepared  farm  manures  as  to  those  in 
commercial  fertilizers. 

INFLUENCE  OF  AGE  AND    KIND  OF  ANIMAL 

187.  Manure  from  Young  and  from  Mature  Animals. 
—  The  manure  from  older  animals  is  somewhat  more 
valuable  than  that  from  young  animals,  even  when  fed 
the  same  kind  of  food.  This  is  because  more  of  the 
phosphoric  acid  and  nitrogen  are  retained  in  the  body 
of  a  young  animal.  It  is  not  so  much  a  difference  in 
digestive  power  as  a  difference  in  retentive  power.  In 
older  animals  the  proportion  of  new  nitrogenous  tissue 
produced  is  much  less  than  in  young  animals,  and  more 


I/O  SOILS   AND    FERTILIZERS 

of  the  nitrogen  of  the  food  is  used  for  repair  purposes 
and  subsequently  voided  in  the  manure,  while  with 
young  animals  more  of  the  nitrogen  is  retained  for  the 
construction  of  new  muscular  tissue. 

When  an  animal  is  neither  gaining  nor  losing  in  flesh, 
and  is  not  producing  milk,  an  equilibrium  is  established 
between  the  nitrogen  in  the  food  supply  and  the  nitro- 
gen in  the  manure,  and  practically  all  of  the  nitrogen 
of  the  food  is  returned  in  the  manure.67 

188.  Cow  Manure.  —  A  milch  cow  when  fed  a  bal- 
anced ration  will  make  from  60  to  70  pounds  of  solid 
and  liquid  manure  a  day,  of  which  20  to  30  pounds  are 
liquid.     The  solid  excrement  contains  about  6  pounds 
of   dry  matter.     When  a   cow  is  fed  clover  hay,  corn 
fodder,  and  grain,  about  half  of  the  nitrogen  of  the  food 
is  in  the  urine,  about  one  fourth  in  the  milk,  and  the  re- 
mainder in  the  solid  excrement.     Hence,  if   the   solid 
excrement  only  is  collected,  but  a  quarter  of  the  nitro- 
gen of  the  food  is  recovered ;  while  if  both  solids  and 
liquids  are   utilized,  three  quarters   of   the   nitrogen  is 
secured.     Cow  manure  is  extremely  variable  in  compo- 
sition and  is  the  most  bulky  of  any  manure  produced  by 
domestic  animals.      A  well-fed  cow  will  produce  about 
80  pounds  of  manure  per  day,  including  absorbents. 

189.  Horse   Manure.  —  Horse   manure   contains   less 
water  than  cow  manure,  and  is  of  a  more  fibrous  na- 
ture, doubtless  due  to  the  horse  possessing  less  power 


FARM    MANURES  I /I 

for  digesting  cellulose  material.  Horse  manure  readily 
ferments  and  gives  off  ammonia  products.  When  the 
manure  becomes  dry,  fire-fanging  results,  due  to  rapid 
fermentation  followed  by  the  growth  of  fungous  bodies, 
and  there  is  a  heavy  loss  of  nitrogen.  Horse  manure 
is  sometimes  considered  of  but  little  value.  This  is 
because  it  so  readily  deteriorates  that  when  used  it  has 
often  lost  much  of  its  nitrogen  by  fermentation.  When 
mixed  with  cow  manure,  both  are  improved,  the  rapid 
fermentation  of  the  horse  manure  is  checked,  and  at 
the  same  time  the  cow  manure  is  improved  in  texture. 
It  is  estimated  that  horses  void  about  three  fifths  of 
their  manure  in  the  stable.  A  well-fed  horse  at  ordi- 
narily hard  work  produces  50  pounds  per  day,  of 
which  about  one  fourth  is  urine.  A  horse  produces 
nearly  6  tons  of  manure  per  year  in  the  stable.  If 
properly  preserved  and  used,  it  is  valuable  and  quick- 
acting;  but  if  allowed  to  ferment  and  leach,  it  gives 
poor  results. 

190.  Sheep  Manure.  —  Sheep  produce  a  small  amount 
of  concentrated  manure,  containing  less  water  than  that 
of  any  other  domestic  animal.  It  readily  ferments  and 
is  a  quick-acting  fertilizer.  When  combined  with  horse 
and  cow  manure  the  mixture  ferments  more  slowly. 
Because  of  the  small  amount  of  water  it  contains,  sheep 
manure  is  very  concentrated  in  composition.  It  is  val- 
uable for  general  gardening  purposes  and  whenever  a 
concentrated,  quick-acting  manure  is  desired. 


SOILS   AND    FERTILIZERS 

191.  Hog  Manure.  —  Hog  manure  is  not  constant  in 
composition  on  account  of  the  varied  character  of  the 
food    consumed.     The    manure    from    fattening   hogs 
which  are  well  fed  compares  favorably  in  composition 
and   value   with  that  produced   by  other  animals.     It 
contains  a  high  per  cent  of  water,  and,  like  cow  ma- 
nure,  may    be  slow  in  decomposing.     On  account  of 
containing  so  much  water,  losses  by  leaching  readily 
occur.     From  a  given  weight  of  grain,   pigs  produce 
less  dry  matter  in  the  manure  than  do  sheep  or  cows. 
The  liquid  excrements  of  well-fed  hogs  are  rich  in  ni- 
trogen,  containing,  on  an  average,  about  2    per  cent. 
The  solids  when  leached,  fermented,  and  deprived  of 
the  liquid  excrements  have  little  value  as  fertilizer. 

192.  Hen   Manure.  —  Like  all   other  farm   manures, 
hen  manure  is  variable  in  composition.     The  nitrogen 
is  mainly  in  the  form  of  ammonium  compounds,  making 
it  a  quick-acting  fertilizer.     When  fowls  are  well  fed 
the  manure  contains  about  the  same  amount  of  nitro- 
gen as  that  of  sheep.     Hen  manure  readily  ferments 
and  if  not  properly  cared   for  losses  of   nitrogen,   as 
ammonia,  occur.     It   is   not  advisable   to  mix  with   it 
hard  wood  ashes  or  ordinary  lime,  because  the  ammo- 
nia is  so  readily  liberated  by  alkaline  compounds.     The 
value  of  hen  manure  is  due  to  its  being  a  quick-acting 
fertilizer  rather  than  to  its  containing  a  large  amount  of 
fertility.     A   hen  produces  about  a  bushel  of   manure 
per  year. 


FARM  MANURES 
COMPOSITION  OF  HEN  MANURE 


PER  CENT 

Water    

C7.CO 

Nitrogen     

1.27 

Phosphoric  acid   

0.82 

Potash    

o  28 

193.  Mixing  of  Solid  and  Liquid  Excrements.  —  The 
solid  and  liquid  excrements  together  make  a  well-bal- 
anced manure.     Urine  alone  is  not  a  complete  manure, 
as  it  is  deficient  in  phosphoric  acid  and  other  mineral 
matter.     The    solid    excrement    and   the   urine,   when 
combined  with  soil,  readily  undergo  nitrification.     The 
nitrogen  in  the  solid  excrement  is  in  the  form  of  indi- 
gestible protein  and  is  rendered  available  more  slowly 
as  plant  food.     Land  dressed  with  leached  manure  re- 
ceives an  unbalanced  fertilizer  deficient  in  nitrogen  but 
fairly  well  supplied  with  mineral  matter  and  may  fail  to 
respond  because  of   the   unbalanced   character   of  the 
manure.     A    large   amount   of    fertility   is   often    lost 
through  poor  and  leaky  stable  floors.     When  the  floors 
and  trenches  are  made  of  cement,  better  sanitary  condi- 
tions   prevail    and   losses    of    fertility   are    prevented. 
The   mixing  of   the  solid   and   liquid   excrements   and 
waste  bedding   should  be  accomplished   in   the   stable 
trenches. 

194.  Volatile  Products  from  Manure.  —  Fermentation 
of  manure  in  stables  results  in  the  production  of  a  large 


1/4  SOILS   AND    FERTILIZERS 

number  of  volatile  compounds  and  in  loss  of  manurial 
value.  When  urea  ferments,  ammonium  carbonate,  a 
volatile  product,  results ;  and  where  the  proteids  of  ma- 
nure ferment,  ammonia  is  formed,  which  combines  with 
the  carbon  dioxide,  always  present  in  stables  in  liberal 
amounts  as  a  product  of  respiration,  to  form  ammonium 
carbonate,  a  volatile  compound.  When  the  stable  at- 
mosphere becomes  charged  with  ammonium  carbonate, 
some  of  it  is  deposited  on  the  walls  of  the  stable, 
forming  a  white  coating.  The  white  coating  found 
on  harnesses  and  carriages  stored  in  poorly  ventilated 
stables  is  ammonium  carbonate.  Accumulations  of 
manure  in  the  stable  and  poor  ventilation  are  the  condi- 
tions favorable  to  its  production. 

195.  Human  Excrements.  —  The  use  of  human  excre- 
ments as  manure  is  sometimes  advised,  and  in  some 
countries  they  are  extensively  so  utilized.  When  fresh, 
they  may  contain  a  high  per  cent  of  nitrogen  and  phos- 
phoric acid ;  but  when  fermented,  a  loss  of  nitrogen  has 
occurred.  Heiden  estimates  1000  pounds  a  year  of 
excrements  per  person,  containing  $2.25  worth  of  fertil- 
ity.59 For  sanitary  reasons,  human  excrements  should 
be  used  as  manure  with  great  care,  and  it  is  doubtful, 
with  the  abundance  and  cheapness  of  plant  food, 
whether  the  practice  is  advisable.  About  1840  Leibig 
expressed  the  fear  that  the  essential  elements  of  plant 
food  would  accumulate  in  the  vicinity  of  large  cities  and 
be  wasted,  and  that  in  time  there  would  be  a  decline  in 


FARM    MANURES 


175 


fertility  due  to  this  cause.60  Many  political  economists 
shared  the  same  fear.  Since  that  time  the  fixation  of 
atmospheric  nitrogen  through  the  agency  of  leguminous 
crops  has  been  discovered,  extensive  beds  of  sodium 
nitrate,  phosphate  rock,  and  Stassfurt  salts  have  been 
utilized,  and  larger  areas  of  more  fertile  soil  have  been 
brought  under  cultivation,  so  that  it  is  not  now  so 
essential  to  devise  means  for  utilizing  human  excre- 
ments as  manure. 


THE  PRESERVATION  OF  MANURE 

196.  Leaching.  —  Leaching  of  manure  is  the  greatest 
source  of  loss.  Experiments  by  Roberts  show  that 
when  horse  manure  is  thrown  in  a  loose  pile  and  sub- 
jected to  the  joint  action  of  leaching  and  weathering  it 
may  lose  in  six  months  nearly  60  per  cent  of  its  most 
valuable  fertilizing  constituents.  The  results  of  these 
experiments  are  tabulated  as  follows : 61 


APRIL  25 
LBS. 

SEPT.  28 
LBS. 

Loss 
PER  CENT 

4OOO.OO 

I73O.OO 

17 

10.  60 

7.7Q 

60 

I4..8O 

7-70 

47 

Potash  

36.00 

8.65 

76 

Value  per  ton      

$2.80 

$1.06 

Cow  manure,  on  account  of  its  more  compact  nature, 
does  not  leach  so  readily  as  horse  manure.     A  similar 


176 


SOILS    AND    FERTILIZERS 


experiment   with   cow  manure,  conducted  at  the  same 
time,  showed  the  following  losses : 


APRIL  25 
LBS. 

SEPT.  28 
LBS. 

Loss 
PER  CENT 

Gross  weight  

IO,OOO 

CI2C 

AQ 

Nitrogen   

A.7 

28 

41 

•\2 

26 

IQ 

Potash  

4.8 

AA 

8 

Value  per  ton      

$2.2Q 

$1.60 

When  mixed  cow  and  horse  manure  was  compacted 
and  "  placed  in  a  galvanized  iron  pan  with  a  perforated 
bottom  "  for  six  months,  the  losses  were  as  follows : 


MARCH  29 
LBS. 

SEPT.  30 
LBS. 

Loss 
PER  CENT 

226.OO 

222.OO 

1.04 

I.OI 

^.2 

Phosphoric  acid    .... 
Potash     

0.61 
i.  20 

0.58 
O.A-i 

47 

7C.O 

Value  per  ton       .... 

$2.38 

$2.  1  6 

197.  Losses  by  Fermentation.  —  When  rapid  fermen- 
tation takes  place  in  manure,  appreciable  losses  of 
nitrogen  may  occur.  When  the  manure  is  well  com- 
pacted and  the  pile  is  so  constructed  as  to  prevent  rapid 
circulation  of  air  through  it,  losses  are  reduced  to  the 
minimum.  Experiments  show  that  when  leaching  is 
prevented,  the  loss  of  nitrogen  by  fermentation  of  mixed 


FARM    MANURES 


177 


manure  is  very  small.  Under  poor  conditions  losses  by 
fermentation  may  exceed  15  per  cent.  Hen  manure, 
sheep  manure,  and  horse  manure  are  the  most  ferment- 
able, particularly  when  fungous  growths  and  molds  are 
formed.  When  extreme  conditions,  as  excessive  mois- 
ture, are  followed  by  drought  and  high  temperature, 
then  the  greatest  losses  occur. 

198.  Different  Kinds  of  Fermentation. — The  large 
number  of  organisms  present  in  manure  all  belong  to 
one  of  two  classes:  (i)  aerobic,  or  (2)  anaerobic.  The 
aerobic  ferments  require  an  abundant  supply  of  air  in 
order  to  carry  on  their 
work.  When  deprived 
of  oxygen,  they  become 
inactive.  The  anaero- 
bic ferments  require 
the  opposite  condition. 
They  become  inactive 
in  the  presence  of  oxy- 
gen and  Can  thrive  Only  FlG'  36-  Fermentation  of  Manure. 

when  air  is  excluded.  In  the  center  of  a  well-constructed 
manure  pile  anaerobic  fermentation  occurs,  while  on 
the  surface  aerobic  fermentation  is  active.  The  anaer- 
obic ferments  prepare  the  way  for  the  action  of  the 
aerobic.  When  aerobic  fermentation  is  completed,  the 
organic  matter  is  converted  into  water,  carbon  dioxide, 
ammonia,  and  allied  gases,  and  these  are  lost.  Conse- 
quently, anaerobic  fermentation  is  the  most  desirable. 


178  SOILS    AND    FERTILIZERS 

The  bacterial  content  of  the  soil  is  greatly  increased 
by  the  use  of  farm  manures,  and  also  food  is  supplied 
to  the  organisms  already  in  the  soil,  many  of  which  take 
an  important  part  in  rendering  plant  food  available. 

199.  Water  Necessary  for  Fermentation.  —  In  order  to 
produce  the  best  results  in  fermenting  manure,  water  is 
necessary ;  for  if  the  manure  becomes  too  dry,  abnormal 
fermentation  takes  place.    Water  is  always  beneficial  on 
manure  so  long  as  leaching  is  prevented,  for  it  encour- 
ages anaerobic  fermentation  by  excluding  the  air.     An 
excess  of  water,  such  as  falls  on  manure  piles  from  the 
eaves  of  buildings,  is  more  than  is  required  for  good 
fermentation.    During  a  dry  time  it  is  beneficial  to  water 
the  compost  pile. 

200.  Heat  produced   during  Fermentation.  —  During 
active  fermentation  of  horse  and  sheep  manure  a  tem- 
perature of  175°  F.  may  be  reached  by  the  fermenting 
mass.      Ordinarily,   however,    the    temperature   of    the 
manure  pile  ranges  from  110°  to  130°  F.     The  highest 
temperature  is  near  the  surface,  where  fermentation  is 
most  rapid.     The  temperature  of  fermentation  may  be 
sufficiently  high  to  cause  spontaneous  combustion,  if  the 
manure  is  mixed  with  litter. 

201.  Composting  Manure  may  improve  its  Quality.  — 

Composting  manure  so  that  leaching  and  rapid  fermen- 
tation do  not  take  place  may  improve  its  quality,  mak- 


FARM    MANURES 


179 


ing  it  more  concentrated.  Pound  for  pound,  composted 
manure  is  richer  in  plant  food  than  fresh  manure,  be- 
cause, if  properly  cared  for,  nearly  all  of  the  nitrogen, 
phosphoric  acid,  and  potash  of  the  original  manure  are 
present  in  smaller  bulk.  A  ton  of  composted  manure  is 
obtained  from  about  2800  pounds  of  stable  manure. 
Composting  is  sometimes  resorted  to  in  order  to  destroy 
obnoxious  weed  seeds. 


FRESH 
MANURE 
PER  CENT 

COMPOSTED 
MANURE 
PER  CENT 

0.50 
0.28 
O.6o 

O.6o 

0-39 
0.8o 

Phosphoric  ncicl  

Potash    

In  composting  manure  it  should  be  the  aim  to  induce 
anaerobic  fermentation  by  excluding  the  air  and  retain- 
ing the  water.  This  can  be  accomplished  best  by  using 
mixed  manure  and  making  a  compact  pile,  capable  of 
shedding  water.  The  compost  pile  should  be  shaded  to 
secure  better  conditions  for  fermentation.  If  the  pile 
becomes  offensive,  a  little  earth  on  the  surface  will 
absorb  the  odors. 

202.  Use  of  Preservatives.  —  The  use  of  preservatives, 
as  gypsum  and  kainit,  has  been  recommended  to  prevent 
fermentation  losses.  Opinions  differ  as  to  the  value  of 
this  practice.  Moist  gypsum,  when  it  comes  in  contact 


ISO  SOILS   AND    FERTILIZERS 

with   ammonium  carbonate,    produces   ammonium   sul- 
phate, a  non-volatile  compound, 


CaSO4  =  (NH4)2SO4  +  CaCO3. 

Gypsum  when  used  should  be  at  the  rate  of  about 
one  half  pound  per  day  for  each  animal.69  Experiments 
show  that  it  prevents  a  loss  of  5  per  cent  of  the  nitro- 
gen of  horse  manure.  It  has  no  action  on  the  feet  of 
animals,  and  so  may  with  safety  be  sprinkled  in  the 
stalls.  When  it  is  necessary  to  use  gypsum  as  a  fertilizer, 
it  is  advantageous  to  use  it  in  stables.  It  is  not  advis- 
able to  use  lime  in  any  other  form  than  the  sulphate. 
Unslaked  lime  will  decompose  manure  and  liberate  am- 
monia. Neither  kainit  nor  gypsum  should  be  used  when 
manure  is  exposed  to  the  leaching  action  of  rains.  Pre- 
servatives cannot  be  made  to  take  the  place  of  care  in 
handling  manure  ;  they  should  be  used  only  when  the 
manure  receives  the  best  of  care. 

203.   Manure  produced  in  Sheds  and  Box   Stalls.  — 

Manure  produced  under  cover,  as  in  sheds  and  box 
stalls,  is  of  superior  quality.  Losses  by  leaching  are 
thus  avoided,  the  manure  is  compacted  by  the  tramping 
of  the  animals,  the  solid  and  liquid  excrements  are  more 
evenly  mixed  with  the  absorbents,  and  the  conditions 
are  favorable  for  anaerobic  fermentation.  By  no  other 
system  is  there  such  a  large  percentage  of  the  fertility 
recovered.  Manure  from  well-fed  cattle,  when  collected 


FARM   MANURES  l8l 

and  prepared  in  a  covered   shed,  will  have  about  the 
following  composition : 


PER  CENT 

Water    

70  oo 

O.QO 

O.6o 

Potash   

O  7O 

Manure  produced  under  cover  has  greater  value  than 
when  cared  for  in  any  other  way.  Experiments  by 
Kinnard  show  that  such  manure  produced  4  tons  more 
potatoes  per  acre  than  pile  manure,  while  n  bushels 
more  wheat  per  acre  were  obtained  on  land  which  had 
the  previous  year  received  the  covered  manure  than  on 
land  which  received  the  uncovered  manure.62  Experi- 
ments at  the  Ohio  Station  show  that  stall  manure  gives 
a  larger  crop  yield  than  yard  manure.98 

THE  USE  OF  MANURE 

204.  Direct  Hauling  to  Fields.  —  It  is  always  desirable, 
whenever  conditions  allow,  to  draw  the  manure  directly 
to  the  field  and  spread  it,  rather  than  to  allow  it  to  ac- 
cumulate about  barns  or  in  the  barnyard.  When  taken 
directly  to  the  field  from  the  stable  no  losses  by  leach- 
ing occur,  and  the  slight  losses  from  fermentation  and 
volatilization  of  the  ammonia  are  more  than  compensated 
for  by  the  benefits  derived  from  the  action  of  the  fresh 


1 82  SOILS   AND    FERTILIZERS 

manure  upon  the  soil.  When  manure  undergoes  fer- 
mentation in  the  soil,  as  previously  stated,  it  combines 
with  the  mineral  matter  of  the  soil  and  produces  humates. 
The  practice  of  hauling  the  manure  directly  to  the  field 
and  spreading  it  with  a  manure  spreader  is  the  most  eco- 
nomical way  of  handling  it,  as  the  manure  is  thus  evenly 
spread,  and  larger  crop  returns  are  secured  from  the 
lighter  and  more  frequent  applications. 

With  scant  rainfall  composting  the  manure  before 
spreading  is  often  necessary,  but  with  liberal  rainfall  it 
is  not  essential.  On  a  loam  soil,  a  direct  application  of 
stable  manure  is  more  advisable  than  on  heavy  clay  or 
light  sandy  soil.  In  the  case  of  sandy  soils  there  is  fre- 
quently an  insufficient  supply  of  water  properly  to  fer- 
ment the  manure.  Manure  on  heavy  clay  land  sometimes 
fails  to  show  any  beneficial  effect  the  first  year  because 
of  the  slow  rate  of  decomposition,  but  the  beneficial 
effects  are  noticeable  the  second  and  third  years. 

When  conditions  will  not  permit  farm  manure  to  be 
hauled  directly  to  the  field  and  spread,  it  should  be 
stored  in  covered  manure  sheds,  so  as  to  prevent  leach- 
ing and  injurious  fermentation. 

205.  Coarse  Manure  Injurious. — The  application  of 
coarse  leached  manure  may  cause  the  soil  to  be  so 
open  and  porous  as  to  affect  the  water  supply  of  the 
crop,  by  introducing  below  the  surface  soil  a  layer  of 
straw,  and  thus  breaking  the  capillary  connection  with 
the  subsoil.  Coarse  manure  and  shallow  spring  plowing 


FARM    MANURES 


are  sometimes  injurious,  where  fine  or  well-composted 
manure  and  fall  plowing  would  be  beneficial.  Trouble 
resulting  from  the  use  of  coarse  manure  may  be  due  to 
its  being  allowed  to  leach  before  it  is  used,  so  that  it 
does  not  readily  ferment  in  the  soil. 

206.  Manuring   Pasture   Land.  —  In   regions    where 
manure  decomposes  slowly,  it  is  sometimes  advisable  to 
use  it  upon  pasture  land  as  a  top  dressing.     The  manure 
encourages  growth  of  the  grass,  so  that  it  appropriates 
plant  food. otherwise  lost;  it  also  acts  as  a  mulch,  pre- 
venting excessive  evaporation.     Then  when  the  pasture 
land  is  plowed  and  prepared  for  a  grain  crop  it  contains  a 
better  store  of  both  water  and  available  plant  food.     The 
manuring  of  pasture  lands  is  one  of  the  best  ways  of  utiliz- 
ing manure  when  trouble  arises  from  slow  decomposition. 

207.  Small  Manure  Piles  Undesirable.  —  It  is  some- 
times the  custom  to  make  a  number  of  small  manure 
piles  in  fields.     This  is  a  poor  practice,  for  it  entails 
additional  ex- 
pense later  in 

spreading  the 
manure,  and 
the  small  piles 
are  usually 
constructed  in 
such  a  way 


FlG.  37.    Manured  Land. 


that  heavy  losses  occur,  so  the  manure,  when  finally 


1 84 


SOILS   AND   FERTILIZERS 


FIG.  38.    Unmanured  Land. 


spread,  is  not  uniform  in  composition.  Oats  grown  on  land 

manured  in  this  way  presented  an  uneven  appearance. 

There  were 
small  patches, 
thrifty  and 
overfed,  cor- 
responding to 
the  places 
formerly  occu- 
pied by  the 

manure  piles,   while   large  areas  of    half-starved  oats 

might  be  observed. 

208.  Rate  of  Application.  —  The  amount  of  manure 
that  should  be  applied  depends  upon  the  nature  of  the 
soil  and  the  crop.  On  loam  soils  intended  for  general 
truck  purposes,  heavier  applications  may  be  made  than 
when  grain  is  raised.  For  general  farm  purposes,  8 
tons  per  acre  are  usually  sufficient.  It  is  better 
economy  to  make  frequent  and  light  applications  than 
heavier  ones  at  long  intervals.  When  manure  is 
spread  frequently  the  soil  is  kept  in  an  even  state 
of  fertility,  and  losses  by  percolation,  denitrification,  and 
ammonification  are  prevented.  Too  often  the  manure 
is  not  evenly  distributed  about  the  farm  ;  fields  adjacent 
to  stables  are  heavily  manured,  while  those  at  a  distance 
receive  none. 

For  growing  garden  crops,  20  tons  and  more  per 
acre  are  sometimes  used.  It  is  better,  however,  not 


FARM   MANURES  185 

to  use  stable  manure  in  excess  for  trucking,  but  to 
supplement  it  with  special  fertilizers  as  the  crops  may 
require.  Soils  which  contain  a  large  amount  of  cal- 
cium carbonate  will  not  become  acid  from  farm  manure, 
and  hence  admit  of  more  frequent  and  heavier  applica- 
tions than  soils  which  are  deficient  in  this  compound. 
The  lime  aids  fermentation  and  nitrification.  Some- 
times a  judicious  combination  of  farm  manure  and 
commercial  fertilizers  can  be  made  that  will  prove 
more  economical  than  farm  manure  alone. 

209.  Crops  Most  Suitable  for  Manuring.  —  Soils  which 
contain  a  low  stock  of  fertility  admit  of  manuring  for 
the  production  of  almost  any  crop.  Soils  well  stocked 
with  plant  food,  like  some  of  the  western  prairie  soils, 
which  are  in  need  of  manure  mainly  for  its  physical 
action,  will  not  allow  its  direct  use  on  all  crops.  On 
a  prairie  soil  of  average  fertility  a  heavy  application 
of  manure  may  cause  wheat  and  other  grain  crops  to 
lodge.  When  manure  cannot  be  applied  directly  to 
a  crop,  it  may  be  used  advantageously  on  a  preced- 
ing crop  and  the  land  thus  be  brought  into  good 
condition  for  the  crop  that  will  not  bear  direct  ma- 
nuring. Manure  never  injures  corn  by  causing  too 
rank  a  growth,  and  wheat  may  follow  corn  which 
has  been  manured  with  but  little  danger  of  loss  from 
lodging. 

On  some  soils  stable  manure  cannot  be  used  for 
growing  sugar  beets ;  on  others  it  does  not  seem  to  exer- 


1 86  SOILS    AND    FERTILIZERS 

cise  an  injurious  effect.  Tobacco  is  injured  as  to  quality 
by  manure.  Flax,  tobacco,  sugar  beets,  and  wheat, 
which  should  not  receive  heavy  direct  applications,  all 
require  manuring  of  the  preceding  crops.  When  in 
doubt  as  to  the  crop  on  which  to  use  the  manure,  it  is 
always  safe  to  apply  it  to  corn,  and  then  to  follow  with 
the  crop  which  would  have  been  injured  by  its  direct 
application. 

That  coarse,  leached  manure  may  cause  trouble  in  a 
dry  season,  and  well-rotted  manure  may  cause  grain  to 
lodge,  are  not  valid  reasons  for  manure  being  wasted  as 
it  frequently  is  in  western  farming,  by  being  burned, 
thrown  away  in  streams,  used  in  making  roads,  or  for 
filling  up  low  places. 

210.  Comparative  Value  of  Forage  and  Manure.  — 
The  manure  from  a  given  amount  of  grain  or  fodder 
always  gives  better  results  than  if  the  food  itself  were 
used  directly  as  manure.  The  manure  from  a  ton  of 
bran  will  give  better  returns  than  if  the  bran  itself 
were  used.  This  is  because  so  little  of  the  fertility 
is  lost  during  the  process  of  digestion,  and  the  action 
of  the  digestive  fluids  upon  the  food  makes  the  manure 
more  readily  available  as  a  fertilizer  than  the  food 
which  has  not  passed  through  any  fermentation  pro- 
cess. It  is  better  economy  to  use  products  as  linseed 
meal  and  cottonseed  meal  for  feeding  stock,  and  then 
take  good  care  of  the  manure,  than  to  use  the  mate- 
rials directly  as  fertilizer. 


FARM   MANURES  l8/ 

211.  Lasting  Effects  of  Manure.  —  No  other  manures 
make  themselves  felt  for  so  long  a  time  as  farm  ma- 
nures.    In  ordinary   farm   practice   an   application   of 
stable  manure  will  visibly  affect  the  crops  for  a  num- 
ber of  years.     At  the  Rothamsted  Experiment  Station, 
records  have  been  kept  for  over  fifty  years  as  to  the 
effects   of   manures    upon    soils.     In   one   experiment, 
farm  manure  was  used  for  twenty  years  and  then  dis- 
continued for  the  same  period.     It  was  observed  that 
when   its   use   was   discontinued  there  was  a  gradual 
decline  in  crop-producing  power,  but  not  so  rapid  as 
of  plots  where  no  manure  had  been  used.    The  manure 
applied  during  the  twenty-year  period  made  itself  felt 
for  an  ensuing  twenty  years. 

212.  Comparative  Value  of  Manure  produced  on  Two 
Farms.  —  The  fact  that  there  is  a  great  difference  in 
the   composition   and   value   of   manures   produced  on 
different   farms   may   be   observed  from  the  following 
examples : 

On  one  farm  10  tons  of  timothy  are  fed.  The 
liquid  manure  is  not  preserved  and  25  per  cent  of  the 
fertility  is  leached  out  of  the  solid  excrements,  while  5 
per  cent  of  the  nitrogen  is  lost  by  volatilization.  It  is 
estimated  that  half  of  the  nitrogen  and  potash  of  the 
food  is  voided  in  the  urine.  On  account  of  the  scant 
amount  and  poor  quality  of  the  food  no  milk  or  flesh 
is  produced. 

On  another  farm  7.5  tons  of  clover  hay  and  2.5  tons 


1 88  SOILS   AND   FERTILIZERS 

of  bran  are  fed.  The  liquid  excrements  are  collected 
and  the  manure  is  taken  directly  to  the  field  and 
spread.  It  is  estimated  that  20  per  cent  of  the  nitro- 
gen and  4  per  cent  of  the  phosphoric  acid  and  potash 
are  utilized  for  the  production  of  flesh  and  milk. 

The  comparative  value  of  the  manure  from  the  two 
farms  is  as  follows  : 

FARM  No.  i 

IN  10  TONS  TIMOTHY 
Lbs. 

Nitrogen 250 

Phosphoric  acid 90 

Potash 400 

Loss  in  Urine 

250  -4-  2  =  125  Ibs.  nitrogen 
400  •*-  2  =  200  Ibs.  potash 

Loss  by  Leaching 

125  x  0.30  =  37.50  Ibs.  nitrogen 
90  x  0.25  =  22.50  Ibs.  phosphoric  acid 
200  x  0.25  =  50  Ibs.  potash 

TOTAL  Loss 
Lbs.  Per  Cent 

Nitrogen 162.5  65 

Phosphoric  acid 22.5  25 

Potash 250.0  62 

PRESENT  IN  FINAL  PRODUCT 
MANURE  FROM  i  TON  TIMOTHY 
Lbs. 

Nitrogen 8.75 

Phosphoric  acid 6.75 

Potash 15.00 

Relative  money  value $r.oo 


FARM    MANURES  189 

FARM  No.  2 

IN  10  TONS  MIXED  FEED 
Lbs. 

Nitrogen 400 

Phosphoric  acid 240 

Potash 300 

Loss,  SOLD  IN  MILK  AND  RETAINED  IN  BODY 
Lbs.  Per  Cent 

Nitrogen,  400  x  0.20 80  20 

Phosphoric  acid,  estimated    .     .     .     10  4 

Potash 12  4 

PRESENT  IN  FINAL  PRODUCT 

MANURE  FROM  i  TON  FEED 

Lbs. 

Nitrogen 32.0 

Phosphoric  acid 23.0 

Potash       29.0 

Relative  money  value $3.80 

213.  Summary  of  Ways  in  which  Stable  Manure 
may  be  Beneficial.  —  Farm  manures  act  upon  soils 
chemically,  physically,  and  bacteriologically. 

(a)  Chemically  : 

1.  By  adding  new  stores  of  plant  food  to  the  soil. 

2.  By  combining  with  the  soil,  forming  humates,  and 
rendering  the  inert  mineral  plant  food  more  available. 

3.  By  raising  the  temperature  of  the  soil,  as  the  re- 
sult of  oxidation. 

(b)  Physically : 

1.  By  making  the  soil  darker  colored. 

2.  By  enabling  soils  to  retain  more  water  and  to  give 
it  up  gradually  to  growing  crops. 


SOILS   AND    FERTILIZERS 


3.  By  improving  the  tilth  of  sandy  and  clay  soils. 

4.  By  preventing  the  denuding  effects  of  heavy  wind 
storms. 

(c)  Bacteriologically  : 

1.  By  increasing  the  number  of  soil  organisms. 

2.  By  promoting  fermentation  changes. 

3.  By  supplying  food  to  the  organisms  which  assist 
in  rendering  plant  food  available. 


CHAPTER  VI 

FIXATION 

214.  Fixation,  a  Chemical  Change.  —  When    a  fer- 
tilizer  is    applied    to    a   soil,  chemical    reaction    takes 
place   between    the   soil  and  the  fertilizer.      There  is 
a  general  tendency  for  the  soluble  matter  of  fertilizers 
to  undergo    chemical    change   and    become   insoluble. 
This  process  is   known  as  fixation.      If   a    solution  of 
potassium  chloride  be  percolated  through  a  column  of 
clay,  the  filtrate  will  contain  scarcely  a  trace  of  potas- 
sium chloride,  but  instead  calcium  and  other  chlorides. 
The  element  potassium  of  the  potassium  chloride  has 
been  replaced  by  the  element  calcium  present  in  the 
soil,  and  as  a  result  of  this  exchange  of  base  elements 
an  insoluble  compound  of  potash  is  formed.     Indepen- 
dent of  chemical  action,  a  small  amount  of  soluble  salts 
are  absorbed  physically  by  soils  and  retained  by  molec- 
ular force.      Absorption  is  a  physical  property  of  soils, 
while  fixation  is  due  to  a  chemical  change. 

215.  Fixation  due  to  Zeolites.  —  It  has  been  shown  by 
experiments,  particularly  those  of  Way  and  Voechler,63 
that  fixation  is  due  mainly  to  zeolitic  silicates.     Sandy 
soils  containing  but  little  clay  have  only  feeble   power 
of  fixation.     Clay  soils  when  digested  with  hydrochloric 

191 


SOILS   AND    FERTILIZERS 

acid  to  remove  the  zeolitic  silicates  lose  their  power  of 
fixation.  The  fixation  of  potassium  chloride  and  the 
liberation  of  calcium  chloride  may  be  illustrated  by  the 
following  reaction : 

Zeolite  Zeolite 

A12031  A12031 

•  (Si02)x.H20  +  2  KC1  =  *2°    \  *(Si02)*-H20  +  CaCl2. 
r  e2vJs 

etc.  etc.  J 

216.  Humus  may  cause  Fixation.  —  Also    other  com- 
pounds of  the  soil,  as  humus  and  calcium  carbonate, 
take  an   important  part  in   fixation.     In   the   case   of 
humus,    a   union    occurs  between  the  minerals  in  the 
fertilizer  and  the  organic  acids  formed  from  the  decay 
of  the  humus  in  the  soil,  resulting  in  the  production  of 
humates. 

217.  Variations  in  Fixative  Power  of  Soils.  —  All  soils 
do  not  possess  the  power  of  fixation  to  the  same  extent. 
Heavy   clays   have  the  greatest   fixative   power,  while 
sandy  soils  have  the  least.     As  a  general  rule,  soils  of 
high  fertility  show  good  fixative  power.      Hence  it  is 
that  a  fertilizer,  after  being  applied  to  a  soil,  may  be 
entirely  changed  in  composition,  so  that  the  plant  feeds 
on  the  chemical  products  formed,  rather  than  on  the 
original  fertilizer. 

218.  Fixation  of  Phosphates.  —  The   phosphates   of 
fertilizers  readily  undergo  fixation  by  combination  with 


FIXATION  193 

the  iron  and  aluminum  compounds  of  soils,  forming  in- 
soluble phosphates.  Experiments  show  that  in  a  loam 
soil  from  2000  to  8000  pounds  per  acre  of  phosphoric 
acid  may  undergo  fixation.  Drainage  waters  contain 
only  traces  of  phosphates.  At  the  Rothamsted  Experi- 
ment Station  the  plots  receiving  an  annual  dressing  of 
phosphates  for  fifty  years  contained  83  per  cent  of  the 
surplus  fertilizer,  half  of  which  was  in  available  forms 
soluble  in  one  per  cent  citric  acid.96 

219.  Fixation  of  Potash. — The  potash  compounds  of 
fertilizers  readily  undergo  fixation,  the  sodium  and  cal- 
cium of  the  soil  being  replaced  by  the  potassium  of  the 
fertilizer.     Drainage  waters  contain  larger  amounts  of 
sodium  than  of  potassium  compounds,  due  to  greater  in- 
solubility of  the  potash  of  the  soil.     Fixation  of  potash 
occurs  mainly  in  the  surface  soil,  where  it  is  held  in 
forms  insoluble    in  water,  a  portion  being  soluble  in 
dilute  acids. 

220.  Nitrates  cannot  undergo  Fixation.  —  Nitrogen  in 
the  form  of  nitrates  or  nitrites  cannot  undergo  fixation. 
This  is  because  all  of  the  ordinary  forms  of  nitrates  are 
soluble.     If  potassium  nitrate  be  added  to  a  soil,  calcium 
or  sodium  nitrate  will  be  obtained  as  the  soluble  com- 
pound.    The  potassium  undergoes  fixation,  but  the  ni- 
trate radical  does  not.     Chlorides  also  are  incapable  of 
undergoing  fixation,  because  all  of  the  chlorides  found 
in  soils  are  soluble. 


IQ4  SOILS   AND    FERTILIZERS 

221.  Fixation  of  Ammonia.  —  Ammonium  compounds 
readily  undergo  fixation,  particularly  in  the  presence  of 
clay.     (See  experiment  No.  17.)     The  ammonium  radi- 
cal, NH4,  like  potassium,  is  capable  of  replacing  soil 
bases.     After  undergoing  fixation,  the  ammonium  com- 
pounds readily  yield  tc    nitrification  (see  Section  1 56), 
hence  they  serve  as  a  temporary  but  important  form  of 
insoluble  nitrogen.     The  general  tendency  of  the  nitro- 
gen compounds  of  the  soil  is  to  pass  from  insoluble  to 
soluble  forms  through  processes  of  decay,  and  to  resist 
fixation  changes. 

222.  Fixation   may    make  Plant   Food   Less  Avail- 
able. —  If  a  very  heavy  dressing  of  potash  or  phosphate 
fertilizer  be  applied  to  a  heavy  clay  soil,  what  is  not 
utilized  the  first  few  years  may  undergo  fixation  to  such 
an  extent  that  part  becomes  unavailable  as  plant  food. 
It  is  not  well  to  apply  unnecessarily  heavy  dressings  of 
fertilizers  at  long  intervals  because  of  fixation.     It  is 
always  best  to  make  light  and  frequent  applications. 

223.  Fixation,  a  Desirable  Property  for  Soils.  —  If  it 
were  not  for  the  process  of  fixation,  soils  in  regions  of 
heavy    rains  would    soon   become    sterile.     When  the 
plant  food  has  become  insoluble,  it  is  retained  in  the 
soil.     That  which  undergoes  fixation  is,  as  a  rule,  in  an 
available  condition  or  may  readily  become  so  by  cultiva- 
tion unless  the  soil  be  one  of  unusual  composition.     The 
process  of  fixation  regulates  the  supply  of  plant  food  in 


FIXATION 


195 


the  soil.  Many  fertilizers,  if  they  did  not  undergo  this 
process,  would  be  injurious  to  crops,  for  there  would  be 
an  abnormal  amount  of  soluble  alkaline  or  acid  com- 
pounds which  would  be  destructive.  When  the  process 


FIG.  39.     Plants  grown  in  Normal  Soil. 

of  fixation  takes  place,  it  removes,  to  a  great  extent, 
injurious  water-soluble  salts,  particularly  when  the  reac- 
tion is  one  of  union  rather  than  replacement.  Then 
the  plant  is  free  to  render  soluble  its  own  food  in  quan- 
tities and  at  times  desired. 

Farm  manures  and  commercial  fertilizers  alike  un- 
dergo the  process  of  fixation  and,  in  studying  ferti- 
lizers, their  action  upon  the  soil  and  the  products  of 
fixation  are  matters  of  prime  importance. 


196 


SOILS   AND   FERTILIZERS 


224.  Soil  Solution.  —  Soil  water  obtained  by  leaching 
soils  is  an  exceedingly  dilute  solution  of  various  mineral 
salts  and  organic  compounds.  Through  rock  disinte- 
gration, mineral  matter  is  rendered  soluble,  but  the  pro- 
cess of  fixation  prevents  accumulation  in  the  soil  solution 


FlG.  40.    Plants  grown  in  Sand  and  watered  with  Leachings  (Soil  Solu- 
tion) from  Soil  as  used  in  Fig.  39. 

of  compounds  of  such  elements  as  potassium  and  phos- 
phorus. As  a  result  of  disintegration  and  fixation, 
numerous  chemical  changes  take  place  in  the  soil,  and 
the  soil  solution  is  an  important  factor  in  bringing  about 
these  changes.  Many  of  the  phenomena  which  have 
been  studied  in  connection  with  solutions  in  physical 
chemistry  take  place  in  the  soil.  Diffusion,  absorption, 
osmotic  pressure,  and  ionization,88  —  disassociation  of  the 
molecule  in  solution,  —  all  occur  in  soils  and  are  due 


FIXATION  197 

largely  to  the  physical  and  chemical  action  of  the  soil 
solution.  The  soil  solution  from  different  soils  varies 
with  the  composition  and  degree  of  disintegration  of 
the  soil  particles,  and  in  the  same  soil  at  different  times 
there  are  variations  in  its  composition.  The  soil  solution 
is  more  important  as  an  agent  for  bringing  about  chem- 
ical and  physical  changes  in  the  soil  than  as  a  store- 
house of  plant  food.  It  is  not  possible  to  exhaust  a  soil 
of  all  of  its  water-soluble  salts  by  one  or  more  leachings. 
There  appears  to  be  a  variable  but  fairly  continuous 
solubility  of  soil  constituents.  King  has  shown  that 
soils  of  high  productiveness  contain  a  larger  amount  of 
soluble  salts  than  soils  of  low  fertility.97 


CHAPTER  VII 


FIG.  4i. 


PHOSPHATE  FERTILIZERS 

225.  Importance  of  Phos- 
phorus as  Plant  Food.  — 
Phosphorus  in  the  form  of 
phosphates  is  one  of  the 
essential  elements  of  plant 
food.  None  of  the  higher 
orders  of  plants  can  complete 
their  growth  unless  supplied 
with  this  element.  The  il- 
lustration (Fig.  41)  shows  an 
oat  plant  which  received  no 
phosphorus  compounds,  but 
was  supplied  with  all  the 
other  elements  of  plant  food. 
As  soon  as  the  phosphoric 
acid  stored  up  in  the  seed 
had  been  utilized,  the  plant 
ceased  to  grow,  and  after  a 
few  weeks,  died  of  phosphate 
starvation,  having  made  the 
total  growth  shown  in  the 
illustration.  All  crops  de- 
mand their  phosphorus  com- 
without  pounds  at  an  early  stage  of 
development.  Wheat  takes 
198 


PHOSPHATE    FERTILIZERS  1 99 

up  80  per  cent  of  its  phosphoric  acid  in  the  first  half  of  the 
growing  period,37  while  clover  has  assimilated  all  it  requires 
by  the  time  the  plant  reaches  full  bloom.43  Phosphorus 
compounds  accumulate,  to  a  great  extent,  in  the  seeds 
of  grains,  and  hence,  when  grain  farming  is  extensively 
followed,  are  sold  from  the  farm.  All  crops  are  very 
sensitive  to  the  absence  of  phosphoric  acid  ;  an  imper- 
fect supply  results  in  the  production  of  light-weight 
grain.  The  nitrogen  and  phosphorus  are  to  a  great 
extent  stored  up  in  the  same  parts  of  the  plant,  par- 
ticularly in  the  seed,  which  is  richer  in  both  of  these 
elements  than  is  any  other  part.  Nitrogen  is  the  chief 
element  of  protein,  while  phosphorus  is  also  necessary 
for  the  formation  of  some  of  the  phosphorus  and  ni- 
trogen compounds,  as  the  nucleo-albumins  and  lecithin. 
Phosphorus  aids  in  the  production  of  the  protein  com- 
pounds. In  speaking  of  the  phosphorus  compounds  in 
plants  and  in  fertilizers,  as  well  as  in  soils,  the  term 
'phosphoric  anhydride'  or  'phosphorus  pentoxide,'  P2O5, 
commonly  called  phosphoric  acid,  is  used.  This  is  be- 
cause phosphorus  is  an  acid-forming  element  and,  as 
already  explained,  the  anhydride  of  the  element  is  al- 
ways considered  instead  of  the  element  itself. 

226.  Amount  of  Phosphoric  Acid  removed  in  Crops.  — 
Grain  crops  remove  about  20  pounds  per  acre  of  phos- 
phoric acid;  the  amount  removed  by  other  farm  crops 
ranges  from  1 8  to  28  pounds,  as  will  be  observed  from 
the  following  table : 


2OO 


SOILS   AND    FERTILIZERS 


PHOSPHORIC  ACID 


PER  ACRE 
LBS. 


Wheat,  20  bu 125 

Straw,  2000  Ibs 7.5 

Total 20.0 

Barley,  40  bu 15 

Straw,  3000  Ibs.  . 5 

Total 20 

Oats,  50  bu 12 

Straw,  3000  Ibs 6 

Total 18 

Corn,  65  bu 18 

Stalks,  4000  Ibs 4 

Total 22 

Peas,  3500  Ibs 25 

Red  clover,  4000  Ibs 28 

Potatoes,  1 50  bu 20 

Flax,  15  bu 15 

Straw,  1800  Ibs 3 

Total    ,                                                         .     .  18 


227.  Amount  and  Source  of  Phosphoric  Acid  in  Soils. 
—  To  meet  the  demand  of  growing  crops  for  about  25 
pounds  of  phosphoric  acid  per  acre,  there  are  present  in 
soils  from  0.03  to  0.25  per  cent.  This  is  equivalent  to 
from  1000  pounds  and  less  to  9000  pounds  per  acre,  of 
which,  however,  only  a  fraction  is  available  as  plant  food  at 


PHOSPHATE   FERTILIZERS  2OI 

any  one  time.  The  availability  of  the  phosphoric  acid  has 
a  great  deal  to  do  in  determining  crop-producing  power. 
Many  soils  contain  a  large  amount  of  total  phosphoric 
acid  which  has  become  unavailable,  because  of  poor  cul- 
tivation and  absence  of  stable  manure  and  lime  to  com- 
bine with  the  phosphates  and  render  them  available. 

The  phosphates  in  soils  are  derived  mainly  from  the 
disintegration  of  phosphate  rock  and  from  the  remains 
of  animal  life.  The  phosphate  deposits  found  in  various 
localities  are  supposed  to  have  had  their  origin  either 
in  the  remains  of  marine  animals  or  sea  water  highly 
charged  with  soluble  phosphates.  These  deposits  have 
been  subjected  to  various  geological  and  climatic  changes 
which  have  resulted  in  the  formation  of  soft  phosphate, 
pebble  phosphate,  and  rock  phosphate.63 

228.  Commercial  Forms  of  Phosphoric  Acid.  —  The 
sources  of  phosphate  fertilizers  are  :  (i)  phosphate  rock, 
(2) bones  and  bone  preparations,  (3)  phosphate  slag,  and 
(4)  guano.  With  the  exception  of  phosphate  slag  and 
guano,  the  prevailing  form  of  phosphorus  is  tricalcium 
phosphate.  Before  being  used  for  commercial  purposes 
the  tricalcium  phosphate,  which  is  insoluble  and  unavail- 
able, is  treated  with  sulphuric  acid,  which  produces  mono- 
calcium  phosphate,  a  soluble  and  available  form. 

Ca3(P04)2  +  2  H2S04  +  5  H20  =  CaH4(PO4)2  +  H2O  + 
2  CaSO4,  2  H2O. 

In  making  phosphate  fertilizers  from  bones  or'phos- 


2O2  SOILS   AND    FERTILIZERS 

phate  rock,  an  excess  of  the  rock  is  used  so  there  will  be 
no  free  acid  in  the  fertilizer  to  be  injurious  to  vegetation. 
As  stated  above,  the  usual  form  in  which  calcium  phos- 
phate is  found  in  nature  is  tricalcium  phosphate, 
Ca3(PO4)2,  and  unless  associated  with  organic  matter 
or  salts  which  render  it  soluble,  it  is  of  but  little  value  as 
plant  food.  When  tricalcium  phosphate  is  treated  with 
sulphuric  acid,  monocalcium  phosphate,  CaH4(PO4)2,  is 
formed,  which  is  soluble  in  water  and  directly  available 
as  plant  food.  When  tricalcium  and  monocalcium  phos- 
phate are  brought  together  in  a  moist  condition,  dical- 
cium  phosphate  is  produced. 


+  CaH/PO^  =  2  Ca2H2(PO4)2. 

Another  form  of  phosphate  of  lime,  met  with  in  basic 
phosphate  slag,  is  tetracalcium  phosphate,  (CaO)4P2O5. 

229.  Reverted  Phosphoric  Acid.  —  When  mono-  and 
tricalcium  phosphate  react,  the  product  is  known  as  re- 
verted phosphoric  acid,  which  is  insoluble  in  water,  but 
is  not  in  such  form  as  to  be  unavailable  as  plant  food  ;  it 
is  generally  considered  available.  Reverted  phosphoric 
acid  may  also  be  formed  by  the  action,  upon  mono- 
calcium  phosphate,  of  iron  and  aluminum  compounds 
present  as  impurities  in  the  phosphate  rock.  As  it  is 
soluble  in  a  dilute  solution  of  ammonium  citrate,  it  is 
sometimes  spoken  of  as  citrate-soluble  phosphoric  acid, 
and  is  not  all  equally  valuable  as  plant  food  because  of 
the  different  phosphate  compounds  that  may  be  dissolved 


PHOSPHATE    FERTILIZERS  2O3 

by  this  solvent.  Citrate-soluble  phosphoric  acid  may  be 
present  in  an  old  fertilizer  in  two  forms,  —  dicalcium 
phosphate  and  hydrated  phosphates  of  iron  and  alumi- 
num. 

230.  Available  Phosphoric  Acid.  —  As  applied  to  fer- 
tilizers, the  term  'available  phosphoric  acid'  includes  the 
water-soluble  and  citrate-soluble  phosphoric  acid.    These 
solvents  do  not,  under  all  conditions,  make  a  sharp  dis- 
tinction as  to  the  available  and  unavailable  phosphoric 
acid  when  it  comes  to  plant  growth.     Some  forms  of 
bone  which  are  insoluble  in  an  ammonium  citrate  solu- 
tion are  available  as  plant  food,  while  some  forms  of 
aluminum  phosphate  which  are  soluble  are  of  but  little 
value.     The  fineness  of  division  of  the  fertilizer  particles 
also  greatly  influences  the  availability  of  the  phosphoric 
acid.  The  terms  '  available '  and  '  unavailable  phosphoric 
acid,'  as  applied  to  commercial  fertilizers,  refer  to  the 
solubility  of  the  phosphates,  and,  as  a  rule,  the  value  of 
the  phosphates  as  plant  food  is  in  accord  with  their  sol- 
ubility —  the  more  insoluble  the  less  valuable. 

231.  Phosphate   Rock.  —  Phosphate  rock  is  found  in 
many  parts  of  the  United  States,  particularly  in  South 
Carolina,  North  Carolina,  Florida,  Virginia,  and  Tennes- 
see.    The    deposits  occur  in  stratified   veins,   as    well 
as   in   beds   and   pockets.     There   are   different   types 
of  phosphates,  as  hard   rock,  soft  rock,  land   pebble, 
and  river  pebble.     The  pebble  phosphates   are  found 


2O4  SOILS   AND    FERTILIZERS 

either  on  land  or  collected  in  cavities  in  water  courses, 
and  are  generally  spherical  masses  of  variable  size. 
Soft  rock  phosphate  is  easily  crushed,  while  the  hard 
rock  requires  pulverizing  with  rock  crushers.  Phosphate 
rock  usually  contains  from  40  to  70  per  cent  of  calcium 
phosphate,  the  equivalent  of  from  17  to  30  per  cent 
phosphoric  acid.  The  remaining  30  to  60  per  cent  is 
fine  sand,  limestone,  alumina,  and  iron  compounds,  with 
other  impurities,  which  often  render  a  phosphate  un- 
suitable for  manufacture  into  high-grade  fertilizer. 

232.  Superphosphate.  —  Pulverized  rock  phosphate, 
known  as  phosphate  flour,  is  treated  with  commercial 
sulphuric  acid  to  obtain  soluble  monocalcium  phosphate. 
The  amount  of  sulphuric  acid  used  is  determined  by  the 
composition  of  the  rock.  Impurities  as  calcium  carbon- 
ate and  calcium  fluoride  react  with  sulphuric  acid  and 
cause  a  loss  of  the  acid.  Ordinarily,  a  ton  of  high-grade 
phosphate  rock  requires  a  ton  of  sulphuric  acid.  The 
mixing  is  done  in  lead-lined  tanks.  A  weighed  amount 
of  phosphate  flour  is  placed  in  the  tank  and  the  sulphuric 
acid  added,  through  lead  pipes,  from  the  acid  tower.  The 
mixing  of  the  acid  and  phosphate  is  done  with  a  mechani- 
cal mixer,  driven  by  machinery.  From  the  mixing  tank 
the  material  is  passed  into  other  large  tanks,  where  two 
or  three  days  are  allowed  for  the  completion  of  the 
reaction.  The  mass  is  placed  in  piles  to  solidify  and  is 
then  ground  and  sold  as  superphosphate.  In  the  manu- 
facture of  superphosphate,  gypsum  (CaSO4.2H2O)  is 


PHOSPHATE    FERTILIZERS 

always  produced.  A  ton  of  superphosphate  prepared 
from  high-grade  rock  in  the  way  outlined  will  contain 
about  40  per  cent  of  lime  phosphate,  equivalent  to  18 
per  cent  phosphoric  acid.  If  a  poorer  quality  of  rock 
is  used,  there  is  a  proportionally  smaller  amount  of  phos- 
phoric acid.  A  more  concentrated  superphosphate  is 
known  as  double  superphosphate  and  is  obtained  by  pro- 
ducing phosphoric  acid  from  the  phosphate  rock,  and 
then  allowing  the  phosphoric  acid  to  act  upon  fresh  por- 
tions of  the  rock,  the  reactions  being  as  follows  :64 

Ca3(P04)2  +  3  H2S04  =  3  CaSO4  +  2  H3(PO4). 
Ca3(P04)2  +  4  H3P04  +  3  H20  =  3[CaH4(PO4)2,  H2O]. 

The  phosphoric  acid  is  separated  from  the  gypsum 
before  acting  upon  the  phosphate  flour.  In  this  way, 
superphosphate  containing  from  35  to  45  per  cent  of 
phosphoric  acid  is  produced.  When  fertilizers  are  to  be 
transported  long  distances,  this  concentrated  product  is 
preferable.  The  terms  '  acid '  and  '  superphosphate ' 
have  been  generally  used  to  designate  the  first  product 
resulting  from  the  action  of  sulphuric  acid  upon  phos- 
phate rock  or  bones,  and  the  term  '  double  superphos- 
phate '  to  mean  the  concentrated  product  formed  by  the 
action  of  phosphoric  acid. 

233.  Commercial  Value  of  Phosphoric  Acid. — The  com- 
mercial value  of  phosphoric  acid  in  fertilizers  is  deter- 
mined by  the  value  of  the  crude  phosphate  rock,  cost 
of  grinding  and  treating  with  sulphuric  acid,  and  cost  of 


2O6  SOILS    AND    FERTILIZERS 

transportation.  The  price  of  phosphoric  acid  in  super- 
phosphates usually  ranges  from  5  to  6  cents  per  pound. 
The  field  value,  that  is  the  increased  yields  obtained 
from  the  use  of  superphosphates,  may  or  may  not  be  in 
accord  with  the  commercial  value  because  so  many  con- 
ditions influence  crop  growth.  The  phosphoric  acid  ob- 
tained from  feed  stuffs  is  usually  considered  worth  about 
a  cent  a  pound  less  than  that  from  superphosphates. 
Water-soluble  phosphoric  acid  is  generally  rated  a  half 
cent  per  pound  higher  than  citrate-soluble  phosphoric 
acid. 

234.  Phosphate  Slag.  —  In  the  refining  of  iron  ores  by 
the  Bessemer  process,  the  phosphorus  in  the  iron  is  re- 
moved as  a  basic  slag.  The  lime,  which  is  used  as  a 
flux,  melts  and  combines  with  the  phosphorus  of  the 
ore,  forming  phosphate  of  lime.  The  slag  has  a  variable 
composition.  The  process  by  which  the  phosphorus  of 
pig  iron  is  removed  and  converted  into  basic  phosphate 
slag  is  known  as  the  Thomas  process,  and  the  product 
is  sometimes  called  Thomas'  slag.  At  the  present  time 
but  little  basic  slag  is  produced  in  this  country  that  is 
suitable  for  fertilizer  purposes.  In  Germany  and  some 
other  European  countries  large  amounts  are  produced 
and  used.  Phosphate  slag  is  ground  to  a  fine  powder 
and  is  applied  directly  to  the  land,  without  undergoing 
the  sulphuric  acid  treatment.  The  phosphoric  acid  is 
present  mainly  in  the  form  of  tetracalcium  phosphate 
(CaO)4P205.  ' 


PHOSPHATE   FERTILIZERS  2O? 

235.  Guano  is  the  Spanish  for  dung  and  is  a  concen- 
trated form  of  nitrogenous  and  phosphate  manure,  of  in- 
terest mainly  on  account  of  its  historic  significance.     It 
is  a  mixture  of  sea-fowl  droppings,  with  dead  animals  and 
debris,  which  have  accumulated  along  the  seacoast  in 
sheltered   regions   and    undergone  fermentation.     The 
introduction  of  guano  into  Europe  marked  an  important 
period  in  agriculture,  inasmuch  as  its  use  demonstrated 
the  action  and  value  of  concentrated  fertilizers.     All  of 
the  best  beds  of  guano  have  been  exhausted  and  only  a 
little  of  the  poorer  grades  is  now  found  on  the  market. 
The  best  qualities  of  guano  contained  from  12  to  15  per 
cent  of  phosphoric  acid,  10  to   12  per  cent  of  nitrogen, 
and  from  5  to  7  per  cent  of  alkaline  salts. 

BONE  FERTILIZERS 

236.  Raw  Bones  contain,  in  addition  to  phosphate  of 
lime,  Ca3(PO4)2,  organic  matter  which  makes  them  slow 
in  decomposing  and  slow  in  their  action  as  a  fertilizer. 
Before   being  used  as  a  fertilizer  they  should  be  fer- 
mented in  a  compost  heap  with  wood  ashes  in  the  follow- 
ing way,  a  protected  place  being  selected  so  that  no  losses 
from  drainage  will  occur.     A  layer  of  well-compacted 
manure  is  covered  with  wood  ashes,  the  bones  are  then 
added  and  well  covered  with  ashes  and  manure.     From 
three  to  six  months  should  be  allowed  for  the  bones  to 
ferment.     The  large,  coarse  pieces  may  then  be  crushed 
and  are  ready  for  use.     The  presence  of  fatty  material 


2O8  SOILS   AND    FERTILIZERS 

in  a  fertilizer  retards  its  action  because  fat  is  so  slow 
in  decomposing.  Bones  from  which  the  organic  matter 
has  been  removed  are  more  active  as  a  fertilizer  than  raw 
bones.  There  is  from  18  to  25  per  cent  of  phosphoric 
acid  and  from  2  to  4  per  cent  of  nitrogen  in  bones. 
The  amount  and  value  of  the  citrate-soluble  phosphoric 
acid  are  extremely  variable. 

237.  Bone  Ash  is  the  product  obtained  when  bones 
are   burned.     It  is  not  extensively  used  as  a  fertilizer 
because  of  the  greater  commercial  value  of  bone  black. 
Bone  ash  contains  about  36  per  cent  of  phosphoric  acid, 
and  is  more  concentrated  than  raw  bones. 

238.  Steamed   Bone.  —  Raw   bones   are   subjected  to 
superheated  steam  to  remove  the  fat  and  ossein  which 
are  used  for  making  soap  and  glue.     They  are  then  pul- 
verized and  sold  as  fertilizer  under  the  name  of  bone  meal, 
which  contains  from  1.5  to  2. 5  per  cent  of  nitrogen  and 
from  22  to  29  per  cent  of  phosphoric  acid.     Steamed 
bone  makes  a  more  active  fertilizer  than  raw  bone.     Oc- 
casionally well-prepared  bone  meal  is  used  for  feeding 
pigs  and  fattening  stock  in  the  same  way  that  flesh  meal 
is  used.     The  fineness  to  which  the  bone  meal  is  ground 
greatly  influences  its  agricultural  value. 

239.  Dissolved  Bone.  —  When  bones  are  treated  with 
sulphuric  acid,  as  in  the  manufacture  of  superphosphates, 
the  product  is  called   dissolved   bone.     The  tricalcium 


PHOSPHATE    FERTILIZERS  2<X) 

phosphate  undergoes  a  change  to  more  available  forms, 
as  described,  and  the  nitrogen  is  rendered  more  available. 
Dissolved  bone  contains  from  2  to  3  per  cent  of  nitrogen 
and  from  15  to  17  per  cent  of  phosphoric  acid. 

240.  Bone  Black.  —  When  bones  are  distilled,  bone 
black  is  obtained.     It  is  extensively  employed  for  refin- 
ing sugar,  and  after  it  has  been  used  and  lost  its  power 
of  decolorizing  solutions  it  is  occasionally  sold  for  fertili- 
zer.    It  is  a  concentrated  phosphate  fertilizer,  containing 
about  30  per  cent  phosphoric  acid. 

241.  Use  of  Phosphate  Fertilizers.  —  The  amount  of 
a  phosphoric  acid  fertilizer  that  it  is  advisable  to  apply 
to  crops  varies  with  the  nature  of  the  soil  and  the  kind 
of  crop  to  be  produced.     On  a  poor  soil  400  pounds  of 
acid  phosphate  per  acre  is  an  average  application.     It  is 
usually  applied  as  a  top  dressing  just  before  seeding,  and 
may  be  placed  near  but  not  in  contact  with  the  seed.    It 
is  not  advisable  to  make  heavy  applications  of  superphos- 
phates at  long  intervals,  because  fixation  may  take  place 
to  such  an  extent  that  crops  are  unable  to  utilize  the 
fertilizer.     Lighter  and  more  frequent  applications,  as 
100  to  200  pounds  per  acre,  are  preferable.    Phosphates 
should  not  be  mixed  with  lime  carbonate  before  spread- 
ing, but  be  applied  directly  to  the  land.22     Phosphates 
may  be  used  in  connection  with  farm  manures.     Many 
soils  which  contain  liberal  amounts  of  phosphoric  acid 
are  improved  by  a  light  dressing  of  phosphates,  75  pounds 


210 


SOILS   AND   FERTILIZERS 


per  acre.  Such  soils,  however,  should  be  more  thor- 
oughly cultivated,  and  manured  with  farm  manures,  to 
make  the  phosphates  available.  There  is  frequently 
an  apparent  lack  of  phosphoric  acid  when  in  reality  the 
trouble  is  due  to  other  causes,  as  a  deficiency  of  lime  or 
organic  matter  to  render  the  phosphates  available.  Be- 
fore using  phosphate  fertilizers,  careful  field  tests  should 
be  made  to  determine  the  needs  of  the  soil. 

242.  How  to  keep  the  Phosphoric  Acid  Available.  — 
Phosphoric  acid  associated  with  organic  matter  in  a 
moderately  alkaline  soil  is  more  available  than  that  in  acid 
soils.  Soft  phosphate  rock  may  be  mixed  with  manure  or 
material  like  cottonseed  meal  and  made  slowly  available 
for  crops,  but  where  land  is  high  in  price  such  a  pro- 
cedure is  not  economical.  Soils  which  contain  a  good 
stock  of  phosphoric  acid,  when  kept  well  manured  and 
occasionally  limed  if  necessary,  have  a  liberal  supply 
of  available  phosphoric  acid.  The  following  is  an 
example  of  two  soils  from  adjoining  farms,  which 
have  been  cropped  and  manured  differently.31 


SOIL  WELL 
MANURED  AND 
CROPS  ROTATED 
PER  CENT 

No  MANURE  AND 
CONTINUOUS  WHEAT 
RAISING 
PER  CENT 

Total  phosphoric  acid  .... 
Humus  

O.2O 

4.2  C 

O.2O 
1.62 

Phosphoric  acid  dissolved  with 

O.o6 

O.O2 

PHOSPHATE   FERTILIZERS  211 

When  the  soil  contains  a  liberal  supply  of  total  phos- 
phoric acid,  it  is  more  economical  to  change  the  phos- 
phoric acid  of  the  soil  to  available  forms  by  the  use  of 
farm  manures,  lime,  rotation  of  crops,  and  thorough 
cultivation,  than  it  is  to  purchase  superphosphates  in  com- 
mercial forms. 


CHAPTER   VIII 


POTASH  FERTILIZERS 

243.  Potassium  an  Es- 
sential Element  of  Plant 
Food.  —  Potassium  is  one 
of  the  three  elements 
most  essential  as  plant 
food.  In  its  absence 
plants  are  unable  to  de- 
velop. Oats  seeded  in 
a  sterile  soil  from  which 
potassium  salts  only  were 
withheld  made  the  total 
growth  shown  in  the  illus- 
tration (Fig.  42).  In  dis- 
cussing the  content  of 
potassium  compounds  in 
plants,  soils,  and  food 
stuffs,  the  term  'potash' 
(potassium  oxide,  K2O) 
is  used.  When  present 
in  the  soil  in  liberal 
amounts  and  associated 
with  other  essential  ele- 

FlG.43.     Oat  Plant  grown  without  Potash,     ments,     potash    produces 

212 


POTASH    FERTILIZERS 


213 


vigorous  plants.  Like  phosphoric  acid  and  nitrogen,  it 
is  utilized  by  crops  in  the  early  stages  of  growth.  It  does 
not  accumulate  in  seeds  to  the  same  extent  as  phosphoric 
acid  and  nitrogen,  but  is  present  mainly  in  stems  and 
leaves ;  consequently  when  straw  crops  are  utilized  in  pro- 
ducing manure,  the  potash  is  not  lost,  or  as  in  the  case  of 
nitrogen,  sold  from  the  farm.  But  with  ordinary  grain 
farming  excessive  losses  of  potash  do  occur,  particularly 
when  the  straw  is  burned  and  the  ashes  are  wasted. 

244.  Amount  of  Potash  removed  in  Crops.  —  In  grain 
crops  from  35  to  60  pounds  of  potash  per  acre  are  removed 
from  the  soil.  For  grass  crops  more  potash  is  required 
than  for  grains,  while  roots  and  tubers  require  more  than 
grass.  The  approximate  amount  of  potash  removed  in 
various  crops  is  given  in  the  following  table  : 


POTASH  PER  ACRB 
K8O 
LBS. 

7 

Straw,  2000  Ibs  

28 

Total      

3"» 

Barley,  40  bu.        

8 

Straw,  3000  Ibs  

^o 

Total      

38 

IO 

Straw,  3000  Ibs.    .          

w 

Total       

4.<; 

214 


SOILS    AND    FERTILIZERS 


POTASH  PER  ACRE 
K,O 
LBS. 


Corn,  65  bu 15 

Stalks,  3000  Ibs 45 

Total 6° 

Peas,  30  bu 

Straw,  3500  Ibs 3^ 

Total 60 

Flax,  15  bu 

Straw,  1800  Ibs 19 

Total 27 

Mangels,  10  tons 150 

Meadow  hay,  i  ton 45 

Clover  hay,  2  tons 66 

Potatoes,  150  bushels 75 


245.  Amount  of  Potash  in  Soils.  —  Ordinarily  there 
is  in  soils  from  o.i  to  0.5  per  cent  of  potash,  equivalent  to 
from  3500  to  18,000  pounds  per  acre  to  the  depth  of 
one  foot.  Many  soils  with  apparently  a  good  stock  of 
total  potash  give  excellent  results  when  a  light  dressing 
of  potash  salts  is  applied.  The  amount  of  available 
potash  in  a  soil  is  more  difficult  to  estimate  than  the 
available  phosphoric  acid.  There  is  much  difference  in 
crops  as  to  their  power  of  obtaining  potash ;  some  re- 
quire greater  help  in  procuring  it  than  others.  A  lack 


POTASH    FERTILIZERS  21 5 

of  available  potash  is  sometimes  indirectly  due  to  a 
deficiency  of  lime  or  other  alkaline  matter  in  the  soil, 
which  prevents  the  necessary  chemical  changes  taking 
place  in  order  that  the  potash  may  be  liberated  as  plant 
food. 

246.  Sources  of  Potash  in  Soils.  —  The  main  source 
of  the  soil's  potash  is  feldspar,  which,  after  disintegra- 
tion, is  broken  up  into  kaolin  and  potash  compounds. 
Mica  and  granite  also,  in  some  localities,  contribute  lib- 
eral amounts,  and  the  zeolitic  silicates  are  a  valuable 
source  of  potash.     There  is  but  little  water-soluble  pot- 
ash except  in  alkaline  soil.     By  the  action  of  many  fer- 
tilizers the  potash  compounds  undergo  changes  in  com- 
position.    For   example,  the  gypsum   which  is  always 
present  in  acid  phosphates  liberates  some  potash.     The 
potash  compounds  of  the  soil  are  in  various  degrees  of 
complexity  from  forms  soluble  in  dilute  acids  to  insoluble 
minerals  as  feldspar. 

247.  Commercial  Forms  of  Potash.  —  Prior  to  the  in- 
troduction of  the  Stassfurt  salts,  wood  ashes  were  the  main 
source  of  potash.     Since  the  discovery  and  development 
of  the  Stassfurt  mines,  the  natural  products,  as  kainit, 
and  muriate  and  sulphate  of  potash,  have  been  exten- 
sively used  for  fertilizing  purposes.     A  small  amount  of 
potash  is  obtained  also  from  waste  products,  as  tobacco 
stems,  cottonseed  hulls,  and  the  refuse  from  beet-sugar 
factories. 


2l6  SOILS    AND    FERTILIZERS 


STASSFURT  SALTS 

248.  Occurrence.64  —  The   Stassfurt  mines    were  first 
worked  with  the  view  of  procuring  rock  salt.     The  va- 
rious compounds  of  potash,  soda,  and  magnesia,  asso- 
ciated with  the  layers  of  rock  salt,  were  regarded  as 
troublesome    impurities,  and    attempts  were  made   by 
sinking  new  shafts  to  avoid  them,  but  with  the  result 
of  finding  them  in  greater   abundance.      About   1864 
their  value  as  potash  fertilizer  was  established.     It  is 
supposed  that  at  one  time  the  region  about  the  mines 
was  submerged  and  filled  with  sea  water.     The  tropi- 
cal climate  of  that  geological  period  caused  rapid  evapo- 
ration, which  resulted  in  forming  mineral  deposits,  the 
less  soluble  material  as  lime  sulphate  being  first  depos- 
ited, then  a  layer  of  rock  salt,  and  finally  layers  of  pot- 
ash and  magnesium  salts  in  the  order  of  their  solubility. 

249.  Kainit   is    a    mineral  composed    of    potassium 
sulphate,  magnesium  sulphate,  magnesium  chloride,  and 
water  of  crystallization.      As  it  comes  from  the  mine 
it  is  mixed  with  gypsum,  salt,   potassium  chloride,  and 
other  bodies.     Kainit  contains  about  1 2  per  cent  potash 
and  is  one  of  the  most  important  of  the  Stassfurt  salts. 
It  is  extensively  used  as  a  potash  fertilizer,  and  is  also 
mixed  with  other  materials  and  sold  as  a  complete  fer- 
tilizer.    The  magnesium  chloride  causes  it  to   absorb 
water,  and  the  presence    of    other   compounds  results 
in  the  formation  of    hard    lumps,  whenever    kainit   is 


POTASH    FERTILIZERS  2I/ 

kept  for  a  long  time.  Kainit  is  soluble  in  water 
and  can  be  used  as  a  top  dressing  at  the  rate  of  75 
to  200  pounds  or  more  per  acre. 

250.  Muriate  of  Potash.  —  This  is  extensively  used  as 
a  fertilizer  and  is  valuable  for  general  garden  and  farm 
crops.     It  is  a  manufactured  product, —  potassium  chlo- 
ride,—  and   ranges  in   purity  from  60  to  95  per  cent, 
equivalent  to  from  35  to  60  per  cent  of  potash,  the 
chief  impurity  being  sodium  chloride.      The  grade  most 
commonly    found    on    the    market    contains    about   50 
per  cent  of    actual    potash,  equivalent  to  80  per  cent 
of  muriate.     Potassium  chloride  is  readily  soluble  and 
is     a    quick-acting   fertilizer.      When    used    in     large 
amounts,  muriate  of  potash  and  other  chlorides  may  un- 
favorably affect  the  quality  of  some  crops,  as  potatoes, 
sugar  beets,  and  tobacco.     Ordinarily,  muriate  of  pot- 
ash is  one  of  the  cheapest  and    most  active  forms  of 
potash,  and  can  be  used  as  a  top  dressing  at  the  rate 
of    200    pounds   or    more    per    acre   when    preparing 
soils  for   crops.      It  is  valuable    for  grass    and    grain 
crops,  and  has  given  good  results  on  peaty  lands.92 

251.  Sulphate  of   Potash.  —  High-grade   sulphate  of 
potash  is  prepared  from  some  of    the  crude  Stassfurt 
salts  and  may  contain  as  high   as  97  per  cent  K2SO4, 
equivalent  to  50  per  cent  of  potassium  oxide  (K2O).     It 
is  one  of   the  most  concentrated  forms  of  potash  fer- 
tilizer and  is    particularly  valuable  because  it    can  be 


218 


SOILS    AND    FERTILIZERS 


applied  safely  to  crops,  as  tobacco  and  potatoes,  which 
would  be  injured  in  quality  if  muriate  of  potash  were 
used,  or  if  much  chlorine  were  present.  Low-grade 
sulphate  of  potash  is  90  per  cent  pure. 

252.  Miscellaneous   Potash   Salts.  —  Carnallit,  9  per 
cent  K2O,  —  composed  of  KCl,MgCl2,6  H2O.     Polyha- 
lit,    15   per  cent  K2O,  —  composed  of    K3SO4,MgSO4. 
(CaSO4)2,H2O.     Krugit,  10  per  cent  K2O,  —  composed 
of  K2SO4,MgSO4,(CaSO4)4,H2O.     Sylvinit,  1 6  to  20  per 
cent    K2O,  —  composed   of   KCl,NaCl    and   impurities. 
Kieserit,  7  per  cent  K2O,  —  composed  of  MgSO4  and 
carnallit. 

253.  Wood   Ashes.  —  For   ordinary  agricultural   pur- 
poses, wood  ashes  are  an  important  source  of  potash, 
although  they  are  exceedingly  variable  in  composition. 
When  leached  the  soluble  salts  are  extracted  and  there 
is  left  only  about  I  per  cent  of  potash.     In  unleached 
ashes  the  amount  of  potash  ranges  from  2  to   10  per 
cent.     Soft  wood  ashes  contain  much  less  potash  than 
hard  wood  ashes.     Goessmann  gives  the  following  as 
the  average  of  97  samples  of  ashes  :  ^ 


AVERAGE 
COMPOSITION 
PER  CENT 

RANGE 
PER  CENT 

Potash  

5-5 

1.9 

34-3 

2-5  to  10.2 

0.3  to   4.0 
18.0  to  50.9 

Phosphoric  acid  

Lime     

POTASH    FERTILIZERS 

IN  10,000  POUNDS  OF  WOOD 


219 


POTASH 
LBS. 

PHOSPHORIC 
ACID 
LBS. 

White  oak      

10.6 

2.C 

14..  O 

6.0 

Ash       

IC.O 

I.I 

Pine      

0.8 

O.7 

Georgia  pine       

c.o 

1.2 

Q.O 

S.7 

254.  Action  of  Ashes  on  Soils.  —  Ashes  act  upon  soils 
both  chemically  and  physically.     They  are  usually  re- 
garded as  a  potash  fertilizer  only,  but  they  also  contain 
lime  and  phosphoric  acid,  and  may  be  very  beneficial 
in  supplying  these  elements.     The  potash  is  present 
mainly  as  potassium  carbonate.     Ashes  are  valuable, 
too,  because  they  add  alkaline  matter  to  the  soil,  which 
corrects  acidity  and  aids  nitrification.     A  dressing  of 
ashes  improves  the  mechanical  condition  of  many  soils 
by  binding  together  the  soil  particles.     This  property 
is  well  illustrated  in  the  so-called  Gumbo  soils,  which 
contain  so  much  alkaline  matter  that  the  soil  has  a  soapy 
taste  and  appearance,  and  when  plowed  the  particles  fail 
to  separate. 

255.  Leached  Ashes.  —  When  ashes  are  leached  the 
soluble  salts  are  extracted ;  the  insoluble  matter  which 
is  left  is  composed  mainly  of  calcium  carbonate  and 
silica.66 


220 


SOILS   AND   FERTILIZERS 


UNLEACHED  ASHES 
PER  CENT 

LEACHED  ASHES 
PER  CENT 

Water    

I2.O 

•3Q  O 

Silica,  etc.       

I3.O 

I  ^.O 

Potassium  carbonate    

5e 

I.I 

Calcium  carbonate  

61  o 

CT  o 

Phosphoric  acid  

I.Q 

}1.V 

1.4. 

256.  Alkalinity  of  Leached  and  Unleached  Ashes.  — 
A  good  way  to  detect  leached  ashes  is  to  determine  the 
alkalinity  in  the  following  way :  weigh  out  2  grams  of 
ashes  into  a  beaker,  add   100  cc.   distilled  water,  and 
heat  on  a  sand  bath  nearly  to  boiling,  cool  and  filter. 
To  50  cc.  of  the  filtrate  add  about  3  drops  of  cochineal 
indicator,  and  then  a  standard  solution  of  hydrochloric 
acid  from  a  burette  until  the  solution  is  neutral.     If  a 
standard  solution  of  acid  cannot  be  procured,  one  con- 
taining 15  cc.  concentrated  hydrochloric  acid  per  liter 
of  distilled  water   may  be  used  for  comparative  pur- 
poses.    Leached  ashes  require  less  than  2  cc.  of  acid 
to  neutralize  the  alkaline  matter  in  I  gram,  while  un- 
leached  ashes  require  from  10  to  18  cc.     In  purchasing 
wood  ashes,  if  a  chemical  analysis  cannot  be  secured, 
the  alkalinity  of  the  ash  should  be  determined. 

257.  Coal  and  Other  Ashes.  —  Since  the  amount  of 
phosphoric  acid  and  potash  in  coal  ashes  is  very  small, 
they  have  little  fertilizer  value.     Soft  coal  ashes  contain 


POTASH    FERTILIZERS 


221 


more  potash  than  those  from  hard  coal,  but  it  is  held  in 
such  firm  combination  as  to  be  of  but  little  value. 

The  ashes  from  sawmills  where  soft  wood  is  burned, 
and  they  are  unprotected,  are  nearly  worthless.  When 
peat  bogs  are  burned  over,  large  amounts  of  ashes  are 
produced.  If  the  bogs  were  covered  with  timber,  the 
ashes  are  sometimes  of  sufficient  value  to  warrant  their 
transportation  and  use. 


POTASH 
PER  CENT 

PHOSPHORIC 
ACID 
PER  CENT 

Hard  coal  ashes   

O  IO 

O  IO 

Soft  coal  ashes          

o  40 

o  40 

Sawmill  ashes  **    

1.  2O 

I.OO 

Peat  bog  ashes  **  

1.  1C 

O.  CA 

Peat  bog  ashes  (timbered)  14      .... 
Tobacco  stem  ash     

3.68 

4..OO 

2.56 

7  OO 

Cottonseed  hulls,  ash    

20  oo 

7  OO 

258.  Commercial  Value  of  Potash.  —  The  market  value 
of  potash  is  governed  by  the  selling  price  of  high-grade 
sulphate  of  potash  and  kainit.  Ordinarily,  it  varies 
from  4  to  5  cents  per  pound.  As  in  the  case  of  nitro- 
gen and  phosphoric  acid,  the  market  and  field  values, 
as  determined  by  crop  yields,  may  be  entirely  at  vari- 
ance. Before  potash  salts  are  used,  careful  field  tests 
should  be  made  to  determine  the  actual  condition  of  the 
soil  as  to  its  need  of  potash.  (See  Chapter  X,  Commer- 
cial Fertilizers.) 


222  SOILS   AND    FERTILIZERS 

259.  Use   of   Potash   Fertilizers.  —  Wood    ashes   or 
Stassfurt  salts  should  not  be  used  in  excessive  amounts. 
Not  more  than  300  pounds  per  acre  should  be  applied 
unless  the  soil  is  known  to  be  markedly  deficient  in 
potash,  and  previous  tests  indicate  that  larger  amounts 
are  safe  and  advisable.     Potash   fertilizers  should  be 
evenly  spread  and  not  allowed  to  come  in  direct  con- 
tact with  plant  roots,  and  should  be  used  early  in  the 
spring   before  seeding  or   before   the  crop  has  made 
much   growth.     Wood   ashes   make   an   excellent  top 
dressing  for  grass  lands,  particularly  where  it  is  de- 
sired to  encourage  the  growth  of  clover.     There  are 
but  few  crops  or  soils  that  are  not  greatly  benefited 
by  a  light  application  of  wood  ashes,  and  none  should 
ever  be  allowed  to  leach  or  waste  about  a  farm. 

260.  Joint  Use  of  Lime  and  Potash.  —  When  a  potash 
fertilizer  is  used,  a  dressing  of  lime  will  frequently  be 
found  beneficial.     The  potash  undergoes  fixation,  and 
when  it  is  liberated  there  should  be  some  basic  material 
as  lime  to  take  its  place.     Goessmann  observed  that 
land  manured  for   several  years  with  potassium  chlo- 
ride finally  produced  sickly  crops,  but  an  application 
of  slaked  lime  restored  a  healthy  appearance  to  suc- 
ceeding crops.67     If  the  soil  is  well  stocked  with  lime, 
its  joint  use  with   potash  fertilizers  is  not  necessary. 
If  it  is  acid,  lime  should  be  used  to  correct  the  acidity 
before  the  potash  is  applied.     The  use  of  potash  fer- 
tilizers for  special  crops  is  discussed  in  Chapter  X 


CHAPTER   IX 
LIME  AND  MISCELLANEOUS  FERTILIZERS 


261.  Calcium  an  Essential 
Element  of  Plant  Food. —  Cal- 
cium is  present  in  the  ash  of 
all  plants,  and  is  usually  more 
abundant  in  soils  than  phos- 
phorus or  potassium.  It  takes 
an  essential  part  in  plant 
growth,  and  whenever  with- 
held growth  is  checked.  The 
effect  of  withholding  calcium 
is  shown  in  the  illustration 
(Fig.  43),  which  gives  the 
total  growth  made  by  an  oat 
plant  under  such  a  condition. 

Plants  grown  on  soils  defi- 
cient in  calcium  compounds 
lack  hardiness.  They  are  not 
so  able  to  withstand  drought 
or  unfavorable  climatic  condi- 
tions as  plants  grown  on  soils 
well  supplied  with  this  element. 
Calcium  does  not  accumulate 
in  the  seeds  of  plants,  but  is 
present  mainly  in  the  leaves 

223 


FIG.  43.    Oat  Plant  grown  with- 
out Calcium. 


224 


and  stems,  where  it  takes  an  important  part  in  the  pro- 
duction of  new  tissue.  The  term  '  lime,'  when  used  in 
connection  with  crops  and  soils,  refers  to  their  content 
of  calcium  oxid,  CaO. 

262.   Amount  of  Lime  removed  in  Crops.38  — 


POUNDS  PER  ACRE 
CaO 


Wheat,  20  bushels 
Straw,  2000  pounds 

Total 

Corn,  65  bushels    . 
Stalks,  3000  pounds 

Total 

Peas,  30  bushels    . 
Straw,  3500  pounds 

Total 

Flax,  15  bushels     . 
Straw,  1800  pounds 

Total 
Clover,  4000  pounds 


I 

2. 

8 

I 

ij. 

12 

4 

71 
75 

3 

_y 

16 

75 


Clover  and  peas  remove  so  much  lime  from  the  soil 
that  they  are  often  called  lime  plants.  The  amount 
required  by  grain  and  hay  is  small  compared  with  that 
required  by  a  clover  or  pea  crop. 

263.  Amount  of  Lime  in  Soils.  —  There  is  no  other 
element  in  the  soil  in  such  variable  amounts  as  cal- 
cium, popularly  called  lime.  It  may  be  present  from 


LIME    AND    MISCELLANEOUS    FERTILIZERS  22$ 

one  hundredth  of  a  per  cent  to  20  per  cent  or 
more.  Soils  which  contain  from  0.3  to  0.5  per  cent, 
as  carbonate,  are  usually  well  supplied.  The  lime  in 
a  soil  takes  an  important  part  in  soil  fertility  ;  when 
it  is  wanting,  humic  acid  may  be  formed,  nitrification 
checked,  and  the  soil  particles  will  lack  binding  mate- 
rial. Calcium  carbonate  is  somewhat  soluble  in  soil 
water,  due  to  the  presence  of  carbon  dioxide.  Waters 
are  hard  because  of  the  presence  of  lime.  The  loss  of 
lime  by  leaching  has  caused  many  soils  to  become 
unproductive. 

264.  Different  Kinds  of  Lime   Fertilizers.  —  By   the 
term    '  lime   fertilizer '   is   usually   meant   land   plaster 
(CaSO4,  2  H2O).      Occasionally  quicklime   (CaO)   and 
slaked  lime  (Ca[OH]2)  are  used  on  very  sour  land.     In 
general,  a  lime  fertilizer  is  one  which  supplies  the  ele- 
ment calcium ;    common  usage,  however,  has  restricted 
the  term  to  sulphate  of  lime. 

265.  Action  of  Lime  Fertilizers  upon  Soils.  —  Lime 
fertilizers  act  both  chemically  and  physically.      Chemi- 
cally,   lime   unites   with   the    organic    matter  to   form 
humate  of   lime   and    thus   prevents    the  formation  of 
humic  acid.     It  also  aids  in  nitrification  and  acts  upon 
the  soil,  liberating  potassium  and  other  elements  of  plant 
food.     Physically,  lime  improves  capillarity,  precipitates 
clay  when  suspended  in  water,  and  prevents  losses,  as 
the  washing  away  of  fine  earth.     When  soils  are  defi- 

Q 


226 


SOILS   AND    FERTILIZERS 


cient  in  lime,  an  acid  condition  may  develop  to  such 
an  extent  as  to  be  injurious  to  vegetation.  Nitrogen, 
phosphoric  acid,  and  potash  may  all  be  present  in  liberal 
amounts,  but  in  the  absence  of  lime  poor  results  are 
obtained.  Because  of  the  loss  by  drainage,  removal 
as  plant  food  and  the  chemical  reaction  in  which  it 
takes  a  part,  there  is  greater  necessity  for  a  liberal 
supply  of  active  lime  compounds  in  a  soil  than  of  any 
other  element  of  plant  food. 

266.  Lime  liberates  Potash.  —  The  action  of  lime 
upon  soils  well  stocked  with  potash  results  in  fixation 
of  the  lime  and  liberation  of  the  potash  ;  the  reaction 
takes  place  in  accord  with  the  well-known  exchange  of 
bases  explained  in  the  chapter  on  fixation.  The  extent 
to  which  potash  may  be  liberated  by  lime  depends  upon 
the  firmness  of  chemical  combination  with  which  the 
potash  is  held  in  the  soil.  Boussingault  found  that 
when  clover  was  limed  there  was  present  in  the  crop 
three  times  as  much  potash  as  in  a  similar  crop  not 
limed.  His  results  are  as  follows  :69 


KILOS  PER  HECTARE 

IN  CROP  NOT  LIMED 

IN  LIMED  CROP 

First 
year 

Second 
year 

First 
year 

Second 
year 

Lime     

32.2 
26.7 
II.O 

32.2 
28.6 
7.0 

794 
95.6 

24.2 

102.8 
97.2 
22-9 

Potash  

Phosphoric  acid       .... 

LIME   AND    MISCELLANEOUS    FERTILIZERS  227 

The  indirect  action  of  land  plaster  upon  western 
prairie  soils  in  liberating  plant  food,  particularly  potash 
and  phosphoric  acid,  is  unusually  marked.  Laboratory 
experiments  show  that  small  amounts  of  gypsum  are 
quite  active  in  rendering  potash,  phosphoric  acid,  and 
even  nitrogen  soluble  in  the  soil  water.5  Occasionally 
applications  of  superphosphate  fertilizers  give  large 
yields,  due  to  the  gypsum  which  they  contain,  and  not 
to  the  phosphorus. 

267.  Quicklime  and   Slaked  Lime.  —  When  it  is  de- 
sired to  correct  acidity,  slaked  lime  is  used.     Air-slaked 
lime  is  not  so  valuable  as  water-slaked  lime.     Quick- 
lime cannot  be  used  on  land  after  a  crop   has   been 
seeded.     Both   slaked   lime   and   quicklime   should   be 
applied  some  little  time  before  seeding,  and  not  to  the 
crop.     The   action  of   quicklime  upon  organic  matter 
is  so  rapid  that  it  destroys  vegetation.     Slaked  lime  is 
less  injurious  to  vegetation. 

268.  Pulverized  Lime  Rock.  —  In  some  localities  pul- 
verized lime  rock  is  used.     It  may  be  applied  as  a  top 
dressing   in   almost    unlimited    amounts.      It  is    most 
beneficial  on  light,  sandy  soils,  where  it  performs  the 
function  of   fine  clay  as  well  as   promoting  chemical 
action.     Acid  soils  also  are  benefited  by  its  use.     Not 
all  soils  are  alike  responsive   to  applications  of  lime- 
stone, and  before  using  it  is  best  to  determine  to  what 
extent  it  is  needed.     There  are  no  ordinary  conditions 


228  SOILS    AND    FERTILIZERS 

where  limestone  is  injurious  to  soil  or  crop,  and  it  is 
frequently  most  helpful. 

269.  Marl.  —  Underlying  beds  of   peat,  deposits  of 
marl   are   occasionally   found.     Marl   is   a   mixture   of 
disintegrated  limestone  and  clay,  and  contains  variable 
amounts   of   calcium   carbonate,    phosphoric   acid,  and 
potash.     When  peat  and  marl  are  found  together,  they 
may  be  used  jointly  with  manure  as  described  in  Sec- 
tion   182.     Many  sandy  lands  in  the  vicinity  of  peat 
and   marl  deposits   would   be   greatly   improved,    both 
physically  and  chemically,  by  these  materials. 

270.  Physical  Action  of  Lime.  —  The  addition  of  lime 
fertilizers  to  sandy  soils  improves  their  general  physi- 
cal condition.     Heavy  clays  lose  their  plasticity  when 
limed  and  the  fine  clay  particles  are  cemented  together 
and  act  as  sand,  which  improves  the  mechanical  con- 
dition of  the  soil.     The  physical  action  of  lime  in  soils 
is  well  illustrated  in  the  case  of  '  loess  soils,'  which  are 
composed   of   clay  and  limestone.     The  lime  cements 
together  the  clay  particles  to  form  compound  grains, 
making  the  soil  more  permeable  and  more  easily  tilled. 
The  better  physical  condition  which  follows  the  appli- 
cation of  lime  fertilizers  is  frequently  sufficient  to  war- 
rant their  use. 

271.  Application  of  Lime  Fertilizers.  —  Lime  is  gener- 
ally used  as  a  top  dressing  on  grass  lands  at  the  rate  of 
200  to  500  pounds  per  acre.     Excessive  applications  are 


LIME   AND    MISCELLANEOUS   FERTILIZERS  229 

undesirable.  Lime  as  gypsum  is  particularly  valuable 
when  applied  to  land  where  crops  are  grown  which 
assimilate  large  amounts,  as  clover  and  other  legumes. 
It  should  be  remembered  that  it  is  not  a  complete 
fertilizer,  but  simply  an  amendment  and  an  indirect 
fertilizer.9  If  used  to  excess  it  may  get  the  soil  in  such 
condition  that  plant  food  is  not  easily  rendered  avail- 
able. A  common  saying  is,  "  Lime  makes  the  father 
rich  but  the  son  poor."  ^  This  is  true,  however,  only 
when  lime  is  used  in  excess.  When  used  occasionally 
in  connection  with  other  manures,  it  has  no  injurious 
effect  upon  the  soil  and  is  a  valuable  fertilizer,  especially 
where  clover  is  grown  with  difficulty. 

MISCELLANEOUS  FERTILIZERS 

272.  Salt  is  frequently  used  as  an  indirect  fertilizer. 
Sodium  and  chlorine,  the  two  elements  of  which  it  is 
composed,  are  not  absolutely  necessary  for  normal 
plant  growth.  When  salt  is  applied  to  the  soil  and 
the  sodium  undergoes  fixation,  potassium  may  be  lib- 
erated. An  early  experiment  of  Wolff  illustrates  this 
point :  a  buckwheat  plot  fertilized  with  salt  produced 
a  crop  with  more  potash  and  less  sodium  than  a  similar 
unfertilized  plot. 

Salt  may  be  used  to  check  the  rank  growth  of  straw 
during  a  rainy  season,  and  thus  prevent  loss  of  the 
crop  by  lodging,  although  not  in  excessive  amounts,  as 
it  is  destructive  to  vegetation ;  200  pounds  per  acre  is  a 


23O  SOILS    AND    FERTILIZERS 

fair  application.  Salt  also  improves  the  physical  con- 
dition of  the  soil  by  increasing  the  surface  tension  of 
the  soil  water.  It  should  not  be  used  on  a  tobacco  or 
potato  crop,  because  it  injures  the  quality  of  the  product. 
Salt  is  beneficial  in  preventing  some  forms  of  fungous 
diseases  from  becoming  established  in  soils. 

273.  Magnesium  Salts.  —  Magnesium  is  present  in  the 
ash  of  all  plants,  and  is  an  element  essential  for  plant 
growth.     Usually  soils  are  so  well  stocked  with  mag- 
nesium  that   it  is  not  necessary  to  apply  it  in  ferti- 
lizers.    Some  of  the  magnesium  salts,  as  the  chloride, 
are  injurious  to  vegetation,  but  when  associated  with 
lime  as  carbonate,  magnesia  imparts  fertility.     In  many 
of  the  Stassfurt  salts,  magnesium  is  found. 

274.  Soot.  —  The  deposits  formed  in  boiler  flues  and 
chimneys  when  wood  and  soft  coal  are  burned  contain 
small  amounts  of  potash  and  phosphoric  acid.     Soot  is 
valuable  mainly  as  a  mechanical  fertilizer  and  is  slow 
in   decomposing.     It   contains  but  little  plant  food  as 
shown  by  the  following  analysis  : 


SOFT  COAL  SOOT 
PERCENT" 

HARD  WOOD  SOOT 
PER  CENT  TO 

Potash    

0.84 

1.78 

Phosphoric  acid   

0.71; 

O.o6 

275.    Seaweeds.  —  Seaweeds  are  rich  in  potash  and 
near  the  seacoast  are  extensively  used  for  fertilizer. 


LIME    AND    MISCELLANEOUS    FERTILIZERS  231 


COMPOSITION  OF 
MIXED  SEAWEEDS 
PER  CENT™ 

\Vater  

81.1:0 

O.77 

Potash  

I.  CO 

Phosphoric  acid      

0.18 

Weeds  and  plants  produced  on  waste  land  along  the 
sea  are  in  some  European  countries  burned  and  the 
ashes  used  as  fertilizer.  By  this  means  waste  land  is 
made  to  produce  fertilizer  for  fields  which  are  tillable. 

276.  Weeds.  —  The  amount  of   fertility  removed   in 
weeds  is  usually  more  than  in  agricultural  plants,  be- 
cause weeds  have  greater  power  of  obtaining  food  from 
the  soil.     When  wheat  or  other  grain  is  raised,  and  a 
small  crop  of  grain  and  a  large  crop  of  weeds  are  the 
result,  there  is  more  fertility  removed  from  the  soil  than 
if  a  heavy  stand  of  grain  had  been  obtained.    The  ashes 
of  strand  plants  and  weeds  are  extremely  variable  in 
composition. 

277.  Wool  Washings  and  Waste.  —  The  washings  from 
wool  contain  sufficient  potash  to  make  them  valuable  as 
fertilizer.     In  wool  there  is  a  high  per  cent  of  potash, 
which  is  soluble  and  readily  removed  in  the  washings. 
Wool  waste  may  contain  from  I  to  5  per  cent  of  potash 
and  from  4  to  7  per  cent  of  nitrogen  in  a  somewhat 
inert  form. 


232  SOILS   AND   FERTILIZERS 

278.  Street  Sweepings.  —  The  horse  manure  and  d& 
bris  collected  from  paved  streets  in  cities  and  known 
as  street  sweepings  have  some  value  as  fertilizer,  and 
are  occasionally  used  for  market  gardening  purposes. 
Street  sweepings,  because  of  the  loss  of  the  liquid 
excrements,  have  a  lower  value  than  average  stable 
manure  and  cannot  be  used  economically  when  labor 
and  the  cost  of  hauling  are  high-priced,  or  when  a 
quick-acting  manure  is  desired.  For  sanitary  reasons, 
the  use  of  street  sweepings  is  not  always  desirable,  as 
mixed  with  the  horse  droppings  frequently  are  associ- 
ated accumulations  of  filth  from  dwellings  contaminated 
with  disease  germs.  Crude  garbage  has  a  low  manurial 
value ;  when  sorted  and  cremated,  the  burned  residue 
can  be  used  to  better  advantage  as  fertilizer  than  the 
raw  garbage,  and  is  without  the  objectionable  and  un- 
sanitary features. 


CHAPTER  X 
COMMERCIAL  FERTILIZERS  AND  THEIR  USE 

279.  Development  of  the  Commercial  Fertilizer  Indus- 
try. —  The  commercial  fertilizer  industry  owes  its  origin 
to  Leibig's  work  on  plant  ash.     The  first  superphos- 
phate was  made  by  Sir  J.  B.  Lawes  about  1840,  from 
spent  bone  black  and  sulphuric  acid.     His  interest  had 
previously  been  attracted  to  the  use  of  bones  as  fer- 
tilizer by  a   gentleman  who  farmed  near  him,   "  who 
pointed  out  that  on  one  farm  bone  was  invaluable  for 
the  turnip  crop,  and  on  another  farm  it  was  useless."  ** 

Since  1860  the  commercial  fertilizer  industry  in  this 
country  has  developed  rapidly,  until  now  large  sums  of 
money  are  annually  expended  in  purchasing  commercial 
fertilizers  and  amendments,  and  nearly  all  in  less  than 
a  third  of  the  area  of  the  United  States. 

280.  Complete    Fertilizers   and   Amendments.  —  The 

term  '  commercial  fertilizer '  is  applied  to  materials  made 
by  mixing  different  substances  which  contain  plant 
food  in  concentrated  forms.  When  a  commercial  fer- 
tilizer contains  nitrogen,  phosphoric  acid,  and  potash, 
it  is  called  a  complete  fertilizer,  because  it  supplies  the 
three  elements  which  are  liable  to  be  most  deficient. 

233 


234  SOILS    AND   FERTILIZERS 

Materials  as  sodium  nitrate  which  supply  only  one  ele- 
ment are  called  amendments.  It  frequently  happens 
that  a  soil  requires  only  one  element  in  order  to  produce 
good  crops,  and  in  such  cases  only  the  one  element 
needed  should  be  supplied. 

Complete  fertilizers  are  often  used  when  the  soil  is 
in  need  of  an  amendment  only. 

281.  Variable  Composition  of  Commercial  Fertilizers. 
—  Since   commercial   fertilizers   are   made    by   mixing 
various  materials  which  contain  different  amounts  of 
nitrogen,  phosphoric  acid,  and  potash,  it  follows  they 
are  extremely  variable  in  composition  and  value.     No 
two  samples  are  the  same,  hence   the  importance  of 
knowing   the   composition   of   every  brand   purchased. 
The  composition  of  fertilizers   is  varied   to   meet  the 
requirements  of  different  soils  and  crops.     Some  ferti- 
lizers are  made  rich  in  phosphoric  acid,  while  others  are 
rich  in  nitrogen  and  potash. 

282.  How  a  Fertilizer  is  Made.  —  The  most  common 
materials  used  in  making  complete  fertilizers  are :  ni- 
trate  of   soda,   kainit,  and  dissolved   phosphate   rock. 
These  materials  have  about  the  following  composition : 

Nitrate  of  soda 15.5  per  cent  nitrogen. 

Kainit 12.5  per  cent  potash. 

Dissolved  phosphate  .    .    .   14.0  per  cent  phosphoric  acid 

The  fertilizer  may  be  made  rich  or  poor  in  any  ingre- 
dient.    Many  fertilizers  contain  about  twice  as  much 


COMMERCIAL    FERTILIZERS   AND   THEIR   USE         235 

potash  as  nitrogen  and  five  times  as  much  phosphoric 
acid  as  potash.  In  order  to  make  a  ton  of  such  a  ferti- 
lizer it  would  be  necessary  to  take : 


POUNDS 

Nitrate  of  soda  

225 

Kainit    

A2C 

Phosphate  

I'JCQ 

The  ton  of  fertilizer  would  contain  about  35  pounds 
of  nitrogen,  189  pounds  of  phosphoric  acid,  and  53 
pounds  potash.  These  amounts  are  determined  by 
multiplying  the  percentage  composition  by  the  weight 
of  material  taken : 

POUNDS 

Nitrogen 225  x  0.155  =    34.9 

Potash 425  x  0.125  =    S3-1 

Phosphoric  acid 1350  x  0.14    =  189.0 

The  fertilizer  would  contain  about  1.75  per  cent  ni- 
trogen, 2.65  per  cent  potash,  and  9.45  per  cent  phos- 
phoric acid.  The  percentage  amounts  are  obtained  by 
dividing  the  total  pounds  by  20.  This  fertilizer  if  made 
at  home  from  materials  purchased  in  the  market,  at  the 
prices  indicated,  would  cost,  exclusive  of  transportation 
and  mixing,  about  $21.47. 

POUNDS  COST 

Nitrogen 34.9  @  16  cents  =  $5.58 

Phosphoric  acid    ....  189.0  @  7  cents  =  13.23 

Potash 53.1  @  5  cents  =    2.66 

Total    $21.47 


236  SOILS    AND    FERTILIZERS 

A  more  concentrated  fertilizer  could  be  prepared  by 
using  high-grade  sulphate  of  potash,  superphosphate, 
and  ammonium  sulphate.  A  fertilizer  composed  of 
these  ingredients  would  contain  : 


POUNDS  PERCENT     TT°™L  VALUE 


T 

LiBS. 

300  Sulphate  of  ammonia  20  N          60  @  16  cents  =  $  9.60     3.00 

500  Sulphate  of  potash  .     50  K2O    250  @    5  cents  =    12.50  12.50 

1200  Superphosphate  .     .     35  P2O5  420  @    7  cents  =    29.40  21.00 

Total    $51.50 

So  concentrated  a  fertilizer  as  the  preceding  is  rarely, 
if  ever,  found  on  the  market,  although  the  price,  $51.50 
per  ton,  is  frequently  charged.  This  example  shows 
the  composition  and  cost  of  the  ingredients  in  one 
of  the  most  concentrated  fertilizers  that  can  be  pro- 
duced. 

The  market  value  of  the  materials  of  which  commer- 
cial fertilizers  are  made  fluctuates  like  that  of  other  com- 
modities. 

Any  of  the  different  materials  mentioned  in  the 
chapters  on  special  fertilizers  can  be  used  in  making 
commercial  fertilizers,  as  dried  blood,  tankage,  nitrate 
of  soda,  sulphate  of  ammonia,  raw  bone,  dissolved 
bone,  raw  phosphate  rock,  dissolved  phosphate  rock, 
basic  slag,  kainit,  muriate  or  sulphate  of  potash,  and 
many  others.  Inasmuch  as  each  of  these  materials 
has  a  different  value,  it  follows  that  fertilizers,  even 


COMMERCIAL    FERTILIZERS   AND    THEIR    USE  237 

of  the   same   general   composition,    may   have    widely 
different  crop-producing  powers. 

283.  Inert  Forms  of  Plant  Food  in   Fertilizers.  —  A 
fertilizer  of  the  same  general  composition  as  the  first 
example,  but  of  different  availability  of   the  elements, 
could  be  made  from    feldspar  rock,  apatite  rock,  and 
leather.      The   leather    contains    nitrogen,   the   apatite 
contains   phosphoric    acid,    and   the    feldspar,    potash. 
Such  a  fertilizer  would  have  no  value  when  used  on  a 
crop,  because  all  the  plant  food  elements  are  present 
in  unavailable  forms.     Hence,  in  purchasing  fertilizers, 
it  is  necessary  to  know  not  only  the  percentage  com- 
position, but  also  the  nature  of  the  materials  from  which 
the  fertilizer  was  made.     Inert  forms  of  plant  food  are 
akin  to  indigestible  forms  of  animal  food ;  it  is  the  food 
which  is  assimilated  that  is  of  value  whether  it  be  by 
animals  or  by  plants. 

284.  Inspection  of  Fertilizers.  —  In  many  states,  laws 
have  been  enacted  regulating  the  manufacture  and  sale 
of   commercial    fertilizers,   and    provision   is    made   for 
inspection  and  analysis  of  all  brands  offered  for  sale. 
The  label  on  the  fertilizer  package  must  specify  the 
percentage  amounts  of  available  nitrogen,  phosphoric 
acid,  and  potash.     Inspection  has  been  found  necessary 
in  order  to  protect  the  farmer  and  the  honest  manu- 
facturer.     As   the   result   of   inspection   and   analysis, 
occasionally  a  fraud  is  revealed  like  the  following : 71 


238  SOILS   AND    FERTILIZERS 

NATURAL  PLANT  FOOD,  $25  TO  $28  PER  TON 


COMPOSITION 

PER  CENT 

Total  phosphoric  acid     

22.21 

Insoluble  phosphoric  acid    

2O  8l 

I.4.O 

O.I7 

Actual  value  per  ton,  $1.52 

285.  Mechanical  Condition  of  Fertilizers.  —  In   pur- 
chasing a  fertilizer  its  mechanical  condition  should  be 
considered.     The  finer  the  fertilizer,  as  a  rule,  the  bet- 
ter it  is  for  promoting  crop  growth.     Some  combina- 
tions of  plant  food  produce  fertilizers  which  become  so 
hard  and  lumpy  that  it  is  difficult  to  crush  them  before 
spreading.     They  should  be  pulverized  so  they  may  be 
evenly  distributed,  otherwise  the  plant  food  will  not  be 
economically  used.     A  fertilizer  that  passes  through  a 
sieve  with  holes  0.25  mm.  in  diameter  is  more  valuable 
and  can  be  used  to  better  advantage  than  one  of  the 
same  composition  with  particles  0.5  mm.  in  size. 

286.  Forms  of  Nitrogen  in  Commercial  Fertilizers. — 
Nitrogen  is  present  in  commercial  fertilizers  in  three 
forms :    (i)    Ammonium    salts,    (2)    nitrates,    and    (3) 
organic    nitrogen.      The    organic    nitrogen    is   divided 
into   two   classes :   (a)   available,   and   (6)  unavailable. 
Pepsin  and  also  potassium   permanganate  are  used  as 
solvents  for  determining  the  availability  of  the  organic 


COMMERCIAL    FERTILIZERS    AND   THEIR    USE 


239 


nitrogen.  The  relative  values  of  the  different  forms 
of  nitrogen  are  discussed  in  Chapter  IV.  Three  fer- 
tilizers may  have  the  same  amount  of  *  total  nitrogen 
and  still  have  entirely  different  crop-producing  powers. 


No.  i 
PER  CENT 

No.  2 
PER  CENT 

No.  3 
PER  CENT 

Nitrogen  as  : 
Ammonium  compounds      .... 

i-75 

O.  I? 

0.25 

O.I  C 

0.10 
O.IO 

Organic  nitrogen  : 
Soluble    

O.  IO 

I.2C 

o.cc 

o.-jc 

UO3 
I.2C 

Total      

2  OO 

2  OO 

2  OO 

In  purchasing  fertilizers  it  is  important  to  know  not 
only  the  amount  of  nitrogen,  but  also  the  form  in 
which  it  is  present.  In  No.  3  the  nitrogen  is  in  an 
inert  form  as  in  leather,  while  in  No.  2  it  is  largely  in 
the  form  of  dried  blood,  and  No.  I  has  mainly  am- 
monium compounds.  Each  of  these  fertilizers,  as  ex- 
plained in  the  chapter  on  nitrogenous  manures,  has  a 
different  plant  food  value. 

287.  Phosphoric  Acid.  —  There  are  three  forms  of 
phosphoric  acid  in  commercial  fertilizers:  (i)  water 
soluble,  (2)  citrate-soluble,  and  (3)  insoluble.  The 
water  and  citrate-soluble  are  called  the  available  phos- 
phoric acid.  In  most  fertilizers  the  phosphoric  acid  is 
derived  from  dissolved  phosphate  rock  and  is  in  the 


240 


SOILS   AND   FERTILIZERS 


form  of  monocalcium  phosphate.  The  citrate-soluble 
is  mainly  dicalcium  phosphate  with  variable  amounts 
of  iron  and  aluminum  phosphates  in  easily  soluble 
forms.  The  insoluble  phosphoric  acid  is  tricalcium 
and  other  phosphates,  as  iron  and  aluminum,  which 
are  soluble  only  in  strong  mineral  acids.  The  insoluble 
phosphoric  acid  in  fertilizers  is  considered  as  having 
but  little  value.  As  in  the  case  of  nitrogen,  three 
fertilizers  may  have  the  same  total  amount  of  phos- 
phoric acid  and  yet  have  entirely  different  values. 


No.  i 
PER  CENT 

No.  2 
PER  CBNT 

No.  3 
PER  CENT 

Water-soluble  phosphoric  acid   .     .     . 
Citrate-soluble  phosphoric  acid  .     .     . 

8.00 
1.50 
o.co 

0.25 
8.00 
I.7C 

0.25 
0.75 
Q.OO 

Total     

IO  OO 

IO.OO 

10.00 

No.  3  has  little  value ;  it  contains  insoluble  phos- 
phate rock  or  some  material  of  the  same  nature.  No.  I 
is  the  most  valuable,  because  it  contains  dissolved 
phosphate  rock  or  dissolved  bone  and  but  little  insoluble 
phosphoric  acid.  No.  2  is  composed  of  such  materials 
as  the  best  grade  of  basic  slag  or  roasted  aluminum 
phosphate  or  fine  steamed  bone. 

288.  Potash.  —  The  three  forms  of  potash  in  fertili- 
zers are:  (i)  water-soluble,  (2)  acid-soluble,  and  (3)  in- 
soluble. Sulphate  of  potash,  kainit,  and  muriate  of 


COMMERCIAL   FERTILIZERS   AND   THEIR   USE  24! 

potash  are  soluble  in  water  and  belong  to  the  first  class. 
In  some  states  the  fertilizer  laws  recognize  only  the 
water-soluble  potash.  In  the  second  class  are  found 
materials  like  tobacco  stems  and  other  organic  forms  of 
potash.  Substances  like  feldspar,  which  contain  insol- 
uble potash,  are  of  no  value  in  fertilizers.  As  a  rule, 
the  potash  in  commercial  fertilizers  is  soluble  in  water ; 
in  only  a  few  cases  are  acid-soluble  forms  met  with. 
Insoluble  potash  is  considered  an  adulterant 

289.  Misleading  Statements  on  Fertilizer  Packages.  — 
Occasionally  the  percentage  amounts  of  nitrogen,  phos- 
phoric acid,  and  potash  are  stated  in  misleading  ways : 
as  ammonia,  sulphate  of  potash,  and  bone  phosphate  of 
lime.     Inasmuch  as  ammonia  contains  14  parts  nitro- 
gen and  3  parts  by  weight  of  hydrogen,  it  follows  the 
ammonia   content  is    proportionally   greater   than   the 
nitrogen  content,  because  of  the  additional   hydrogen 
carried   by   the  ammonia.     And   so   with   sulphate   of 
potash,  which  contains  about  50  per  cent  potash  and  50 
per  cent  of  sulphuric  anhydride.     This  method  of  stat- 
ing the  composition  can  be  considered  in  no  other  way 
than  as  a  fraud,  especially  when  the  fertilizer  contains 
no  sulphate  of  potash,  but  cheaper  materials,  and  the 
phosphoric  acid  is  not  derived  from  bone. 

290.  Estimated   Commercial  Value  of   Fertilizers.— 

The  estimated  value  of  a  commercial  fertilizer  is  ob- 
tained from  the  percentage  composition  and  the  trade 


242  SOILS   AND   FERTILIZERS 

value  of  the  materials  used.     Suppose  two  fertilizers 

are  selling  at  $28  and  $35,  respectively,  each  having  a 
different  composition,  the  estimated  value  of  each  could 
be  obtained  in  the  following  way  : 

COMPOSITION  OF  FERTILIZERS 

No.  i  No.  2 

SELLING  PRICE  $28       SELLING  PRICE  $35 

PER  CENT  PER  CENT 

Nitrogen  as  nitrates 1.50  2.10 

Phosphoric  acid,  available     .     .     .  8.00  10.00 

Phosphoric  acid,  insoluble    .     .     .  2.00  0.50 

Potash  (water-soluble)     ....  2.00  3.50 

POUNDS  PER  TON 


Nitrogen     .     .     . 
Phosphoric  acid    . 
Potash    .... 

No.  i 

1.50  x  20  =    30 
8.00  x  20  =  160 
2.00  x  20  =    40 

No.  a 
2.IO  X  2O  =     42 
IO.OO  X   2O  =  2OO 
3.50  X  20  =     70 

ESTIMATED  VALUE 

No.  i  No.  2 

Nitrogen     .     .     .     .     30  x  0.16  =  $  4.80  42  x  0.16  =  $  6.72 

Phosphoric  acid   .     .   160  x  0.07  =    11.20  200  x  0.07  =    14.00 

Potash 40  x  0.05  =      2.00  70  x  0.05  =      3.50 

$18.00  $24.22 

Difference  between  estimated  value  and  selling  price :  No.  I, 
$10.00;  No.  2,  $10.78. 

The  trade  value  of  a  commercial  fertilizer  often  varies 
widely  from  the  actual  or  crop-producing  value,  for  in 
assigning  a  trade  value  simply  the  cost  of  the  ingredi- 
ents is  considered,  and  this  is  not  necessarily  identical 


COMMERCIAL    FERTILIZERS    AND    THEIR    USE 


243 


with  the  actual  value  secured  in  increased  yield  from 
the  use  of  the  fertilizer. 

291.  Home  Mixing  of  Fertilizers.  —  At  the  New 
Jersey  Experiment  Station  it  was  shown  that  "the 
charges  of  the  manufacturers  and  dealers  for  mixing, 
bagging,  shipping,  and  other  expenses  are  on  the  aver- 
age $8.50  per  ton,  and  also  that  the  average  manu- 


FlG.  44.    Composition  of  Fertilizers. 

factured  fertilizer  contains  about  300  pounds  of  actual 
fertilizing  constituents  per  ton.  These  figures  are  prac- 
tically true  of  other  states,  where  large  quantities  of 
commercial  fertilizers  are  used."  ^  In  states  where 
smaller  amounts  are  used  the  difference  between  the 
estimated  cost  and  selling  price  is  greater  than  $8.50. 

These  facts  emphasize  the  economy  of  home  mixing. 
The  difference  in  price  between  the  raw  materials  and 
the  product  sold  is  frequently  so  great  that  it  is  an  ad- 
vantage for  the  farmer  to  purchase  the  raw  materials, 
as  sulphate  of  potash,  nitrate  of  soda,  and  acid  phos- 


244 


SOILS   AND    FERTILIZERS 


phate,  and  mix  them  as  desired.  By  so  doing  fertilizers 
of  any  composition  maybe  prepared  and  there  is  less  dan- 
ger of  securing  an  inferior  article.  Of  course  it  is  not 
possible  by  means  of  shovels  and  sieves  to  accomplish  as 
thorough  mixing  of  the  ingredients  as  with  machinery. 


Nitrate  of  soda  . 
Acid  phosphate  . 
Sulphate  of  potash 

Total    . 


Nitrate  of  soda  . 
Acid  phosphate  . 
Sulphate  of  potash 
Plaster,  etc.  .  . 

Total    . 


Nitrate  of  soda  . 
Acid  phosphate  . 
Sulphate  of  potash 
Plaster,  etc.  .  . 

Total    . 


FORMULA  No.  i 

POUNDS 

,  500  containing  nitrogen  . 
,  1 200  containing  phos.  acid  . 
,  300  containing  potash  .  . 


FORMULA  No.  2 
250     containing  nitrogen 
900    containing  phos.  acid 
450    containing  potash  . 
400 


POUNDS 

77-5 
1 68.0 
150.0 

395-5 


38.7 
126.0 


FORMULA  No.  3 
200     containing  nitrogen 
1500     containing  phos.  acid 
1 50    containing  potash  . 
150 


316.0 


O  O  a. 

2PH 


3-8? 
8.40 
7.50 


1.99 
6.30 
225.0     11.50 


3897 


31.0       1.55 

2IO.O       10.50 

75-o      5-75 


292.  Fertilizers  and  Tillage.  —  Commercial  fertilizers 
cannot  be  made  to  take  the  place  of  good  tillage,  which 
is  equally  as  important  when  fertilizers  are  used  as  when 


COMMERCIAL   FERTILIZERS   AND    THEIR   USE  24$ 

they  are  omitted.  Scant  crops  are  as  frequently  due  to 
the  want  of  proper  tillage  as  to  the  absence  of  plant 
food.  Poor  cultivation  results  in  getting  the  soil  out  of 
condition;  then,  instead  of  thoroughly  preparing  the 
land,  commercial  fertilizers  are  resorted  to,  and  the 
conclusion  is  reached  that  the  soil  is  exhausted,  when  in 
reality  it  is  suffering  for  the  want  of  cultivation,  for  a 
dressing  of  land  plaster,  for  farm  manures,  or  for  a 
change  of  crops.  There  is  no  question  but  what  better 
tillage,  better  care  and  use  of  farm  manures,  culture  of 
clover  and  systematic  rotation  of  crops  would  result  in 
greatly  reducing  the  amount  annually  spent  for  com- 
mercial fertilizers,  without  reducing  the  yield  of  crops, 
as  well  as  securing  larger  returns  for  the  fertilizers  used. 
In  general,  the  better  the  cultivation  the  less  the  amount 
of  commercial  fertilizer  required  for  average  farm  crops. 
Cultivation  cannot,  however,  entirely  take  the  place  of 
fertilizers. 

293.  Abuse  of  Commercial  Fertilizers.  —  When  a  soil 
produces  poor  crops,  a  complete  fertilizer  is  frequently 
used  where  only  an  amendment  is  needed.  Restricted 
crop  production  on  long-cultivated  prairie  soils  is  often 
due  to  poor  physical  condition,  deficiency  of  humus  and 
available  nitrogen,  or,  in  some  cases,  to  lack  of  a  mineral 
element  as  potash  or  phosphoric  acid.  If  the  nitrogen 
is  supplied  by  legumes,  and  the  one  element  of  fertility 
needed  is  added,  improved  cultivation  together  with  the 
chemical  action  of  the  humus  on  the  minerals  of  the  soil 


246  SOILS   AND   FERTILIZERS 

will  generally  furnish  the  necessary  available  plant 
food.  Instead,  however,  of  providing  the  one  element 
needed,  others  which  may  already  be  present  in  the  soil 
in  liberal  amounts  are  often  supplied  at  an  unnecessary 
expense,  instead  of  being  made  available  by  cultivation. 
Another  abuse  of  fertilizers  is  their  application  to  the 
wrong  crop.  A  heavy  application  of  potash  fertilizer  to 
a  wheat  crop  grown  on  a  rich  clay  soil,  or  of  nitrate  of 
soda  on  land  seeded  to  clover,  or  of  land  plaster  to  flax 
grown  on  a  limestone  soil,  would  be  a  waste  of  money. 

294.  Judicious  Use  of  Fertilizers.  —  In  order  to  make 
the  best  use  of  commercial  fertilizers,  both  the  soil  and 
the  crop  must  be  carefully  considered.  All  soils  do  not 
alike  respond  to  commercial  fertilizers,  and  farm  crops 
possess  different  powers  of  assimilating  food ;  turnips, 
for  example,  have  very  restricted  power  of  phosphate 
assimilation,  hence  they  require  phosphate  manures,  and 
wheat  may  need  help  in  obtaining  its  nitrogen.  A 
wheat  crop  will  starve  for  want  of  nitrogen,  while  an 
adjoining  corn  crop  will  scarcely  feel  its  need.  Wheat 
has  strong  power  of  assimilating  potash,  while  clover 
has  less.  Hence  in  the  use  of  fertilizers  the  ability  of 
the  plant  to  obtain  its  food  must  be  considered.  A 
light  application  of  either  a  special  purpose  or  a  com- 
plete fertilizer  at  the  time  of  seeding  is  often  advanta- 
geous, as  it  encourages  plant  growth  by  supplying  food 
when  it  is  most  needed.  There  should  be  some  at  this 
time  in  a  highly  available  condition  for  the  use  of  the 


COMMERCIAL    FERTILIZERS    AND    THEIR    USE 


247 


young  plants,  after  that  stored  up  in  the  seed  has  been 
exhausted,  and  before  they  are  strong  enough  to  make 
available  their  own  food. 


FIG.  45.    Wheat  Plots  fertilized  in  Different  Ways. 

(From  left  to  right.) 

Complete  Fertilizer  (Com.).        Phosphate  Fertilizer,  P. 

Potash  Fertilizer,  K.  Nitrogen  Fertilizer,  N. 

No  Fertilizer,  Check. 

Commercial  fertilizers  may  assist  in  promoting  desir- 
able bacterial  changes  in  soils  resulting  in  the  elabo- 
ration of  plant  food.  Before  they  are  used,  however, 
careful  field  trials  should  be  made. 


295.    Experimental  Plots.  —  A  piece  of  land  well  tilled 
and  of  uniform  texture  should  be  used  for  field  trials 


248 


SOILS   AND    FERTILIZERS 


with  fertilizers.  After  preparation  for  the  crop,  small 
plots  1/20  of  an  acre  are  staked  off.  A  convenient  size 
is,  length  204  feet,  width  10  feet  8  inches,  area  2176 
square  feet.  Between  each  plot  a  strip  3  feet  wide  is 
left.  The  plan  is  to  apply  one  element  or  a  combina- 
tion of  elements  to  a  plot  and  compare  the  results  with 
plots  differently  treated.70 

296.  Preliminary  Trial.  —  It  is  best  to  make  a  prelim- 
inary trial  one  year  and  verify  the  conclusions  the  next. 
In  making  the  tests,  eight  plots  are  necessary  and  fer- 
tilizers are  applied  in  the  following  way : 

The  first  plot  receives  no  fertilizer  and  is  used  as  the 
basis  for  comparison. 

The  second  plot  receives  a  dressing  of  8  pounds  nitrate 
of  soda,  1 6  pounds  acid  phosphate,  and  8  pounds  sul- 
phate or  muriate  of  potash. 

The  third  plot  receives  nitrogen  and  phosphoric 
acid. 

The  fourth  plot  receives  nitrogen  and  potash. 

The  fifth  plot  receives  nitrogen. 

The  sixth  plot  receives  phosphoric  acid  and  potash. 

The  seventh  plot  receives  potash. 

The  eighth  plot  receives  phosphoric  acid. 


No  fertilizer 

N 

N 

N 

P-jOs 

P206 

K20 

K20 

I 

2 

3 

4 

COMMERCIAL    FERTILIZERS    AND    THEIR    USE 


249 


N 

PzOs 

K2O 

P205 

K20 

5 

6 

7 

8 

Should  good  results  be  obtained  on  plot  No.  3,  the 
indications  are  that  there  is  a  deficiency  of  the  two 
elements,  nitrogen  and  phosphoric  acid.  An  increased 
yield  from  No.  4  indicates  deficiency  of  nitrogen  and 
potash.  Under  such  conditions  the  use  of  a  complete 
fertilizer  would  be  unnecessary.  If  No.  5  gives  an  ad- 
ditional yield,  the  soil  is  in  want  of  nitrogen.  From 
the  eight  plots  it  will  be  seen  which  of  the  various  ele- 
ments it  is  advisable  to  use.  The  fertilizers  should  be 
applied  after  the  land  has  been  thoroughly  prepared  and 
before  seeding.  Corn  is  a  good  crop  for  the  first  trial. 
The  number  of  plots  may  be  increased  by  using  well- 
prepared  stable  manure  and  gypsum  on  plots  9  and  10, 
respectively.  The  second  year  the  results  should  be 
verified. 

297.  Deficiency  of  Nitrogen.  —  If  the  results  indicate 
a  deficiency  of  nitrogen,  select  two  crops,  one  as  wheat, 
which  is  particularly  benefited  by  dressings  of  nitrogen, 
and  another  as  corn  which  has  less  difficulty  in  obtain- 
ing this  element.  The  cultivation  of  each  crop  should 
be  that  which  experience  has  shown  to  be  the  best.  On 
one  wheat  and  one  corn  plot  8  pounds  of  nitrate  of 
soda  should  be  used,  a  plot  each  of  wheat  and  corn  being 


25O  SOILS   AND    FERTILIZERS 

left  unfertilized.  If  both  the  corn  and  the  wheat  are 
benefited  by  the  nitrogen,  the  soil  is  in  need  of  this  ele- 
ment. If,  however,  the  wheat  responds  and  the  corn 
does  not,  the  soil  is  not  in  great  need  of  nitrogen,  but 
does  not  contain  an  abundance  in  available  forms. 

298.  Deficiency  of  Phosphoric  Acid.  —  In  experiment- 
ing  with    phosphoric  acid,  turnips  are  grown  on  two 
plots  and  barley  on  two  plots.     To  one  plot  of  each,  16 
pounds  of  acid  phosphate  are  applied.     If  both  crops 
show  additional  yields,  the  soil  is  in  need  of  available 
phosphoric  acid.     If  only  the  turnips  respond  while  the 
barley  is   indifferent,  the  soil  contains  a   fair  amount. 
Barley  and  turnips  are  used  because   there  is  such   a 
marked  difference  in  their  power  to  assimilate  phosphoric 
acid. 

299.  Deficiency  of  Potash.  —  In  order  to  determine  the 
condition  of   the  soil  as  to   potash,  potatoes  and  oats 
may  be  used  as  the  trial  crops,  and  8  pounds  of  sulphate 
of  potash  should  be  applied  to  one  plot  of  each.     Addi- 
tional yields  indicate  a  poverty  of  available  potash ;  an 
increased  potato  crop  and  an  indifferent  oat  crop  indicate 
potash  not  in  the  most  available  form.     If  no  additional 
yields  are  obtained  with  either  crop,  the  soil  is  not  in 
need  of  potash. 

300.  Deficiency  of  Two  Elements.  —  If  the  preliminary 
trial  indicates  a  deficiency  of  two  elements,  as  nitrogen 
and  phosphoric  acid,  in  verifying  these  results,   both 


COMMERCIAL    FERTILIZERS   AND    THEIR   USE  25 1 

elements  are  used  together,  in  the  same  way  as  de- 
scribed for  deficiency  of  nitrogen,  with  additional  plots 
for  the  separate  application  of  nitrogen  and  phosphoric 
acid. 

301.  Importance  of  Field  Trials.  —  While  it  is  a  diffi- 
cult matter  to  determine  the  actual  needs  of  a  soil,  it 
will  be  found  that  both  time  and  money  are  saved  by  a 
systematic  study  of  the  question.     Suppose  fertilizers 
are  used  in  a  '  hit  or  miss '  way  year  after  year  on  a 
soil  deficient  only  in  phosphoric  acid,  it  might  take  eight 
years  to  indicate  what  the  soil  really  lacks  if  a  different 
fertilizer  is  used  each  year,  and  during  all  this  period 
either  the  soil  fails  to  receive  its  proper  fertilizer,  or 
expensive    and    unnecessary    plant    food   is   provided. 
Field  tests  to  be  of  value  must  be  continued  for  a  num- 
ber of  years  and  the  results  verified. 

302.  Will  it  pay  to  use   Commercial  Fertilizers?  — 

This  question  can  be  answered  only  by  trial.  If  a  soil 
is  in  need  of  available  plant  food,  the  additional  yield 
should  pay  for  the  fertilizer  and  the  expense  of  using 
it.  Some  fertilizers  have  an  influence  on  two  or  three 
successive  crops,  and  only  partial  returns  are  received 
the  first  year.  When  large  crops  must  be  produced  on 
small  areas,  as  in  truck  farming,  commercial  fertilizers 
are  generally  necessary.  They  have  not  yet  been  ex- 
tensively used  in  the  western  prairie  states  in  the  pro- 
duction of  large  tracts  of  staple  crops,  as  wheat  and  corn. 


252  SOILS   AND    FERTILIZERS 

If  there  is  a  good  stock  of  natural  fertility  in  the  soil 
and  it  is  well  tilled,  with  farm  manures  used  and  the 
crops  systematically  rotated,  commercial  fertilizers  will 
not  be  needed.  With  poor  cultivation  and  a  soil  that 
has  been  impoverished  by  injudicious  cropping,  they 
are  necessary.  Commercial  fertilizers  sometimes  fail 
to  give  good  results  because  of  an  excessively  acid  or 
alkaline  condition  of  the  soil. 

303.  Amount  of  Fertilizer  to  use  per  Acre.  —  When 
commercial  fertilizers  are  used  in  general  farming,  just 
enough    should  be  applied  to  produce   normal  yields. 
Heavy   applications  at  long  intervals  are  not  so  pro- 
ductive of  good  results  as  light  applications  more  fre- 
quently.    From  400  to  600  pounds  per  acre  is  as  much 
as  should  be  used  at  one  time  unless  previous  trials 
have   shown    that   heavier   applications  are  necessary. 
The  way  in  which  the  fertilizer  is  to  be  applied,  as 
broadcast  or  otherwise,  must  be  determined  by  the  crop 
to  be  grown.     The  fertilizer  should  not  come  in  contact 
with  seeds,  neither  should  it  be  plowed  under  nor  worked 
into  the  soil  to  such  a  depth  that  it  may  be  lost  by  leach- 
ing before  it  can  be  appropriated  by  the  crop. 

304.  Excessive  Applications  of  Fertilizers  Injurious.  — 
An  overabundance  of  plant  food  has  an  injurious  effect 
upon  crop  growth.     Plants  take  their  food  from  the  soil 
in  dilute  solutions,  and  when  the  solution  is  concentrated 
abnormal   growth   results.     Potatoes    heavily   manured 


COMMERCIAL    FERTILIZERS    AND    THEIR    USE 

with  nitrate  of  soda  produce  luxuriant  vines,  but  only 
a  few  small  tubers.  When  a  medium  dressing  is  used 
along  with  potash  and  phosphoric  acid,  a  more  balanced 
growth  and  better  yield  result. 

Heavy  applications  of  nitrate  of  soda  produce  a  rank 
growth  of  straw,  with  a  low  yield  of  grain.  The  excess 
of  nitrogen  causes  the  mineral  matter  to  be  utilized  for 
straw  and  leaves  only  a  small  amount  for  grain  produc- 
tion. When  applications  of  commercial  fertilizers  are 
too  heavy,  plants  take  up  unnecessary  amounts  of  food 
and  fail  to  make  good  use  of  it.  In  fact,  crops  may  be 
overfed,  or  fed  an  unbalanced  ration,  the  same  as  ani- 
mals. Hence  in  the  use  of  fertilizers  excessive  and  un- 
balanced applications  are  to  be  avoided. 

305.  Fertilizing  Special  Crops.  —  There  are  crops 
which  need  special  help  in  obtaining  some  one  element, 
and  in  using  fertilizers  the  rule  should  be  to  help  those 
crops  which  have  the  greatest  difficulty  in  obtaining 
food.  When  the  soil  does  not  show  a  marked  defi- 
ciency in  any  one  element,  light  dressings  of  special 
purpose  manures  may  be  made  to  the  following  crops  : 

Wheat.  —  Nitrogen  first,  then  phosphoric  acid.  In 
the  case  of  some  soils,  phosphoric  acid  and  potash  pro- 
duce larger  yields  than  nitrogen. 

Barley,  oats,  and  rye  require  manuring  like  wheat,  but 
to  a  less  extent.  Each  crop  has  a  different  power  of 
assimilating  nitrogen.  Wheat  requires  the  most  help 
and  barley  and  rye  the  least. 


254  SOILS   AND   FERTILIZERS 

Corn.  —  Phosphoric  acid  first,  then  nitrogen  and 
potash. 

Potatoes.  —  General  manuring,  reenf orced  with  pot- 
ash. 

Mangels.  —  Nitrogen. 

Turnips.  —  Phosphoric  acid. 

Clover.  —  Lime  and  potash. 

Timothy.  —  General  manuring. 

306.   Commercial  Fertilizers  and   Farm    Manures.  — 

Commercial  fertilizers  should  not  replace  farm  manures, 
but  simply  reenforce  them.  Although  commercial  fer- 
tilizers are  called  complete  manures,  they  fail  to  supply 
organic  matter.  It  is  more  important  in  some  soils 
than  in  others  that  the  organic  matter  be  maintained, 
because  in  some  soils  the  organic  matter  takes  a  more 
important  part  in  crop  production  than  does  the  food 
applied  in  commercial  forms.  When  a  rich  prairie  soil 
is  reduced  by  grain  cropping  and  is  allowed  to  return  to 
pasture,  heavier  yields  of  grain  are  afterward  obtained 
than  from  similar  land  which  has  received  only  appli- 
cations of  commercial  fertilizers.  This  is  due  to  the 
action  of  the  humus  in  the  soil.  At  the  Canadian  Do- 
minion Experimental  Farms,  where  comparative  trials 
have  been  made  for  eighteen  years  with  farm  manures 
and  commercial  fertilizers,  it  has  been  found  that  farm 
manures,  even  on  new  lands,  give  better  results  than 
commercial  fertilizers  for  the  production  of  wheat  and 
corn.98 


CHAPTER   XI 

FOOD   REQUIREMENTS   OF   CROPS 

307.  Amount  of  Fertility  removed  by  Crops.  —  The 
amount  of  fertility  removed  from  an  acre  of  soil  pro- 
ducing average  crops  varies  between  wide  limits.  For 
example,  an  acre  of  mangels  removes  150  pounds  of 
potash,  while  an  acre  of  flax  removes  27  pounds ;  an 
acre  of  corn  removes  75  pounds  of  nitrogen,  while 
an  acre  of  wheat  removes  35  pounds.  Crops  which 
remove  the  most  fertility  do  not  always  require  the  most 
help  in  obtaining  their  food.  This  is  because  the 
amount  of  plant  food  assimilated  is  not  a  measure  of 
the  power  of  crops  to  obtain  food.  An  acre  of  corn 
requires  over  twice  as  much  nitrogen  as  an  acre  of 
wheat,  but  wheat  often  leaves  the  soil  in  a  more  im- 
poverished condition  than  corn,  because  corn  has  greater 
power  to  procure  nitrogen  and  utilize  that  formed  by 
nitrification  after  the  wheat  crop  has  completed  its 
growth.  The  available  nitrogen  if  not  utilized  by  a  crop 
may  be  lost  in  various  ways.  Mangels  require  twice  as 
much  phosphoric  acid  as  flax,  but  are  a  strong  feeding 
crop  and  need  less  help  in  obtaining  this  element.  It 
was  formerly  believed  the  plant  food  in  the  matured 
crop  indicated  the  kind  and  amount  of  fertilizing  ingredi- 
ents to  apply,  and  that  a  correct  system  of  manuring 

255 


256 


SOILS   AND    FERTILIZERS 


required  a  return  to  the  soil  of  all  elements  removed  in 
the  crop.     Experiments  show  this  view  to  be  incorrect. 

POUNDS  PER  ACRE  OF  PLANT  FOOD  REMOVED  BY  CROPS  38 


Crops 

Gross 
weight 

Nitro- 
gen 

Phos- 
phoric 
acid 

Potash 

Lime 

Silica 

Total 
ash 

Wheat,  20  bu.     .     . 

I2OO 

2OOO 

25 
IO 

I2.S 
7.? 

7 
28 

I 

7 

I 
lie 

25 
185 

10;> 

Total  .... 

•JC 

2O 

^? 

8 

116 

2IO 

Barley,  40  bu.     .     . 
Straw    

I92O 
3000 

28 
12 

15 

5 

8 
3° 

i 
8 

12 
60 

40 
I76 

Total  .... 

AO 

20 

^8 

Q 

72 

216 

Oats,  50  bu.  .     .     . 
Straw    

1000 

•?ooo 

35 

I  C 

12 

6 

IO 
"K 

i-5 
Q.I; 

15 
60 

55 

I  ?O 

Total      .    . 

CO 

18 

AC 

I  I.O 

7C 

20  c 

Corn,  65  bu.  .     .     . 
Stalks   

22OO 
3000 

3U 
40 

35 

18 

2 

*o 

15 

45 

i 
ii 

13 

I 
89 

^u> 

40 

160 

Total       .     .     . 

7C 

2O 

60 

12 

DO 

200 

Peas,  30  bu.  .     .     . 
Straw    

I8OO 
-JCOO 

/3 

18 

7 

22 
38 

4 

71 

yu 
I 

64 
176 

Total  .... 

2C 

60 

7C 

IO 

24.O 

Mangels,  10  tons     . 
Meadow  hay,  i  ton 
Clover  hay,  2  tons  . 
Potatoes,  150  bu.    . 
Flax,  15  bu.  .     .     . 
Straw  

2OOOO 
2OOO 
4OOO 
9OOO 
9OO 
I800 

75 
3° 

40 
39 
15 

35 

20 
28 
20 
15 

3 

ISO 

45 
66 

75 
8 

19 

3° 

12 

75 
25 
3 
13 

IO 

5° 
15 
4 
0.5 

3 

35° 
'75 
250 
125 
34 
53 

Total      .     .     . 

CA 

18 

27 

16 

•7.C 

87 

FOOD  REQUIREMENTS  OF  CROPS         257 

For  example,  an  acre  of  wheat  contains  35  pounds  of 
nitrogen,  while  an  acre  of  clover  contains  70  pounds ; 
if  70  pounds  of  nitrogen  were  applied  to  an  acre  of 
clover  and  35  pounds  to  an  acre  of  wheat,  poor  results 
would  follow,  because  clover  can  obtain  its  own  nitrogen 
while  wheat  is  less  able  to  do  so,  and  the  35  pounds 
would  not  necessarily  come  in  contact  with  the  roots 
so  that  all  could  be  assimilated.  While  the  amount  of 
plant  food  removed  in  crops  cannot  serve  as  the  basis 
for  their  manuring,  valuable  results  are  obtained  from  a 
study  of  the  different  elements  of  fertility  which  they 
contain.  In  making  use  of  the  preceding  table,  other 
factors,  as  the  influence  of  the  crop  upon  the  soil  and 
the  power  of  the  crop  to  obtain  its  food,  must  also  be 
considered. 

308.  Plants  exert  a  Solvent  Power  in  Obtaining 
Food.  —  It  is  believed  that  crops  procure  some  of  their 
food  from  minerals  insoluble  in  water.  Experiments 
by  Liebig  demonstrate  that  plants  have  the  power  of 
rendering  a  portion  of  their  food  soluble,  provided  it 
does  not  exist  in  forms  too  inert  to  undergo  chemical 
change.  Liebig  grew  barley  in  boxes  so  constructed 
that  all  of  the  water-soluble  plant  food  could  be  secured. 
Two  of  the  boxes  were  manured  and  two  left  unmanured. 
In  one  box  which  received  manure  and  one  which 
received  none,  barley  was  grown.  One  each  of  the 
manured  and  unmanured  boxes  was  left  barren.  He 
collected  all  of  the  drain  waters  and  determined  the 


SOILS   AND    FERTILIZERS 

soluble  mineral  matter  present,  also  weighed  and  analyzed 
the  plants.  His  results  showed  that  92  per  cent  of  the 
potash  was  obtained  from  forms  insoluble  in  water.78 

The  soluble  plant  food  from  a  fertile  soil  is  not  gen- 
erally sufficient  for  plant  growth.85  When  oats,  wheat, 
and  barley  were  seeded  in  prepared  sand  and  watered 
with  the  teachings  from  a  pot  of  fertile  soil,  they  made 
only  a  limited  growth.  Oats  grown  in  prepared  sand 
and  watered  with  soil  leachings  assimilated  only  25  per 
cent  as  much  phosphoric  acid  as  plants  grown  in  fertile 
soil.  See  Section  224.  The  character  and  concentra- 
tion of  the  soil  solution  are,  however,  important  factors 
in  crop  production  and  some  soils  may  contain  sufficient 
amounts  of  water-soluble  elements  to  produce  crops.  The 
relative  amounts  of  food  which  plants  take  from  the 
soil  solution  and  that  which  they  render  soluble  have 
not  been  extensively  investigated. 

In  the  roots  of  plants  there  are  various  organic  acids 
and  salts.  Between  the  root  and  the  soil  is  a  layer  of 
water.  The  plant  sap  and  the  soil  water  are  separated 
by  plant  tissue,  which  serves  as  a  membrane.  All  of  the 
conditions  are  favorable  for  osmosis.  The  sap  from  the 
roots  finds  its  way  into  the  soil  in  exchange  for  some  of 
the  soil  water.  The  acid  and  other  compounds,  excreted 
by  the  roots,  act  upon  the  mineral  matter,  rendering 
portions  of  it  soluble,  and  then  it  is  taken  up  by  the 
plant.  Different  plants  contain  different  kinds  and 
amounts  of  solvents,  as  well  as  present  different  areas  of 
root  surface  to  act  upon  the  soil,  and  the  result  is  that 


FOOD  REQUIREMENTS  OF  CROPS         259 

agricultural  crops  have  different  powers  of  assimilating 
food.  This  action  of  living  plant  roots  upon  soils  is  a 
digestion  process  which  is  somewhat  akin  to  the  diges- 
tion of  food  by  animals. 

Plants  not  only  possess  the  power  of  rendering  a  por- 
tion of  their  food  soluble,  but  they  are  also  able  to  select, 
and  to  reject  that  which  is  unnecessary.  For  example, 
wheat  grown  on  prairie  soil  with  soda  in  equally  abun- 
dant and  soluble  forms  as  the  potash  will  contain 
relatively  little  soda  compared  with  the  potash ;  also 
many  seaweeds  contain  more  potash  than  soda,  although 
the  sea  water  in  which  they  grow  has  an  excess  of 
sodium  salts. 

For  the  feeding  of  crops,  a  nutritive  soil  solution  is 
desirable,  and  the  soil  should  have  a  good  stock  of 
reserve  material  that  can  be  utilized  either  by  action  of 
the  plant  roots  or  readily  pass  into  solution  in  the  soil 
water. 

CEREAL  CROPS 

309.  General  Food  Requirements.  —  Cereal  crops  con- 
tain a  high  per  cent  of  silica  and  evidently  possess  the 
power  of  feeding  upon  some  of  the  simpler  silicates  of 
the  soil,74  liberating  the  base  elements  and  using  them  as 
food,  while  the  silica  is  deposited  in  the  outer  surface  of 
the  straw.  As  previously  stated,  cereal  crops,  although 
they  do  not  remove  large  amounts  of  total  nitrogen  from 
the  soil,  require  special  help  in  obtaining  this  element. 
There  is,  however,  a  great  difference  among  the  cereals  as 


260 


SOILS    AND    FERTILIZERS 


to  power  of  assimilating  nitrogen.  Next  to  nitrogen  they 
stand  most  in  need  of  phosphoric  acid.  There  exists  in 
many  soils  a  greater  deficiency  of  available  phosphoric 
acid  and  potash  than  of  nitrogen,  although,  in  general, 
cereal  crops  are  better  able  to  procure  these  elements 
than  they  are  nitrogen.  The  humic  phosphates  are 
utilized  by  nearly  all  the  cereals. 

310.  Wheat.  —  This  crop  is  more  exacting  in  its  food 
requirements  than  barley,  oats,  or  rye.  It  is  compara- 
tively a  weak  feeding  crop,  and  the  soil  should  be  in  a 
higher  state  of  fertility  than  for  other  grains.  The  ex- 
tensive experiments  of  Lawes  and  Gilbert  give  valuable 
information  regarding  the  effects  of  manures  on  wheat. 
Their  results  are  given  in  the  following  table  :  "5 

AVERAGE  YIELD  OF  WHEAT  PER  ACRE 


BUSHELS 


No  manure  for  40  years  .... 
Minerals  alone  for  32  years  .  .  . 
Nitrogen  alone  for  32  years  .  .  . 
Farmyard  manure  for  32  years  .  . 
Minerals  and  nitrogen  for  32  years1 
Minerals  and  nitrogen  for  32  years2 


'Si 

23* 


'86  pounds  of  nitrogen  as  sodium  nitrate. 
1 86  pounds  of  nitrogen  as  ammonium  salts. 

The  food  requirements  of  wheat  are  such  that  it  should 
be  given  a  favored  position  in  the  rotation.  It  may  follow 
clover,  provided  the  clover  sod  is  light  and  is  fall  plowed. 


FOOD    REQUIREMENTS    OF    CROPS  26 1 

On  some  soils,  however,  wheat  does  not  thrive  following 
a  sod  crop,  as  it  takes  nearly  a  year  for  a  heavy  sod 
residue  to  get  into  suitable  food  forms  for  a  wheat  crop, 
and  under  such  a  condition,  oats  should  first  be  sown, 
then  wheat  may  follow.  On  average  soil,  a  medium 
clover  sod,  plowed  late  in  summer  or  in  early  fall,  and 
followed  by  surface  cultivation,  leaves  the  land  in  good 
condition  for  spring  wheat.  It  is  not  advisable  to  have 
wheat  follow  barley,  because  the  soil  will  be  too  porous, 
and  barley  being  a  stronger  feeding  crop  leaves  the  land 
in  a  poor  state  as  to  available  plant  food.  When  corn 
has  been  well  manured,  wheat  may  follow.  The  food  re- 
quirements of  wheat  are  best  satisfied  following  a  light, 
well-cultivated  clover  sod,  or  following  oats,  which  have 
been  grown  on  heavy  sod,  or  following  corn  that  has 
been  well  manured.  When  wheat  is  judiciously  grown 
in  a  rotation  and  farm  manures  are  used,  it  is  not  an  ex- 
hausting crop.  Light  dressings  of  farm  manure  may 
be  used  on  land  that  is  being  prepared  for  wheat.  On 
many  western  prairie  soils,  dressings  of  phosphate  and 
potash,  either  alone  or  in  combination,  materially  increase 
the  yield  and  improve  the  quality  of  the  crop.  Potash 
fertilizers  have  a  tendency  to  produce  strong  bright 
straw  that  is  more  resistant  to  fungous  diseases.  Nitro- 
gen alone  does  not  give  as  good  results  as  when  com- 
bined with  minerals. 

311.    Barley.  — While  wheat  and  barley  belong  to  the 
same  general  class  of  cereals,  they  differ  greatly  in  their 


262 


SOILS   AND   FERTILIZERS 


habits  and  food  requirements.  Barley  is  a  stronger 
feeding  crop,  has  greater  root  development  near  the 
surface,  and  can  utilize  food  in  cruder  forms.  In  many 
of  the  western  states,  soils  which  produce  poor  wheat 
crops,  from  too  long  cultivation,  give  excellent  yields  of 
barley.  This  is  due  to  changed  conditions,  of  both  the 
chemical  and  mechanical  composition  of  the  soil.  Long 
cultivation  has  made  the  soil  porous,  and  reduced  the 
nitrogen  content.-  Barley  thrives  best  on  a  rather  open 
soil,  and  has  greater  nitrogen  assimilative  power  than 
wheat.  Barley,  however,  responds  liberally  to  manur- 
ing, particularly  to  nitrogenous  manures.  The  experi- 
ments of  Lawes  and  Gilbert  on  the  growth  of  barley  are 
briefly  summarized  in  the  following  table  : 76 

AVERAGE  YIELD  OF  BARLEY  PER  ACRE  FOR  34  YEARS 


BUSHELS 

17v 

Superphosphate  alone    

21-r 

Mixed  minerals    

24.1 

Nitrogen  alone     

•JOf- 

Nitrogen  and  superphosphate      

AC 

Farmyard  manures   

AQi 

312.  Oats.  —  Oats  can  obtain  food  under  more  ad- 
verse conditions  than  either  barley  or  wheat.  They  are 
also  less  exacting  as  to  the  physical  condition  of  the 
soil.  The  oat  plant  will  adapt  itself  to  either  sandy  or 
clay  soil,  and  will  thrive  in  the  presence  of  alkaline 


FOOD  REQUIREMENTS  OF  CROPS          263 

matter  or  humic  acid  where  wheat  would  be  destroyed. 
In  a  rotation,  oats  usually  occupy  a  position  less  fa- 
vored by  manures ;  they  are,  however,  greatly  benefited 
by  fertilizers,  particularly  those  of  a  nitrogenous 
nature.  The  oat  crop  responds  liberally  to  manuring. 
Light  dressings  of  farm  manure  can  be  applied  directly 
to  oat  land  when  well  worked  into  the  soil  before 
seeding. 

313.  Corn.  —  Experiments  with  corn  indicate  that 
under  ordinary  conditions  it  requires  most  help  in 
obtaining  phosphoric  acid.  Corn  removes  a  large 
amount  of  gross  fertility,  and  if  its  production  is  long- 
continued  without  the  use  of  manures  it  impoverishes 
the  soil.  Its  habits  of  growth,  however,  are  such  that  it 
generally  leaves  an  average  prairie  soil  in  better  me- 
chanical condition  for  succeeding  crops.  Corn  is  not 
injured  as  are  many  grain  crops  by  heavy  applications 
of  stable  manure,  and  does  not,  like  flax,  produce  waste 
products  which  are  destructive  to  itself.  The  conditions 
are  better  for  wheat  culture  after  one  or  two  corn  crops 
have  been  removed  from  rich,  newly  broken  prairie  soil. 
The  food  requirements  of  corn  are  satisfied  by  applica- 
tions of  stable  manure,  occasionally  reenforced  with 
a  little  nitrogen  and  phosphoric  acid,  and  in  the  case  of 
some  soil  potash.  After  clover,  corn  gives  excellent 
returns,  and  when  corn  is  the  chief  market  crop  it 
should  be  favored  by  having  the  best  position  in  the 
rotation. 


264  SOILS    AND    FERTILIZERS 

MISCELLANEOUS    CROPS 

314.  Flax  is  very  exacting  in  food  requirements  and 
for  its  culture  the  soil  must  be  in  a  high  state  of  fertility. 
It  is  a  type  of  weak  feeding  crop.     There  are  but  few 
roots  near  the  surface  and  consequently  it  has  restricted 
power  of   nitrogen    assimilation.38     Flax  should   be  in- 
directly manured.     Direct  applications  of  stable  manure 
produce  poor  crops,  but  when  the  manure  is  applied  to 
the  preceding  crop,  excellent  results  are  obtained.     Flax 
does   not   remove   a   large   amount   of   fertility,  but  if 
grown  too  frequently  the  tendency  is  to  get  the  land  out 
of  condition,  rather'than  to  exhaust  it.     The  best  condi- 
tions for  flax  culture  require  that  it  should  be  grown  on 
the  same  land  only  once  in  five  years.     Flax  straw  does 
not  form  suitable  manure  for  flax  lands.     Dr.  Lugger 
demonstrated  that  there  are  produced,  when  the  roots 
and  straw  of  flax  decay,  products  which  are  destructive 
to  succeeding  flax  crops.77     Also  flax  diseases  are  intro- 
duced into  land  by  the  use  of  diseased  flax  seed.     The 
food  requirements  of  flax  are  met  when  it  follows  corn 
which  has  been  well  manured,  or  a  sod  which  has  been 
given   the   cultivation  described  for  wheat.     Flax  and 
spring  wheat  are  much  alike  in  food  requirements. 

315.  Potatoes.  —  Potatoes   are   surface   feeders,   and 
when  grown  continuously  upon  the  same  soil  without 
manure,  the  yield  per  acre  decreases  more  rapidly  than 
that  of  any  other  farm  crop.     Experiments  with  pota- 


FOOD    REQUIREMENTS    OF    CROPS 


265 


toes  by  Lawes  and   Gilbert,  using   different   manures, 
gave  the  following  results:78 

AVERAGE  YIELD  PER  ACRE  FOR  12  YEARS 


TONS 

CWT. 

I 
3 
3 

2 

5 
4 

I9| 

5 
71 

171 

31 

Superphosphate                

Nitrate  of  soda  alone      

Mixed  manures  and  nitro°ren  

Farm  manures,  alternate  years      

Potatoes  require  liberal  general  manuring  reenforced 
with  wood  ashes  or  other  potash  fertilizer.  In  the  rota- 
tion they  should  follow  grain  or  pasture,  provided  the 
fertility  of  the  soil  is  kept  up.  Commercial  fertilizers 
for  potato  production  should  contain  a  fair  amount  of 
available  nitrogen  (2  to  3  per  cent)  and  a  more  liberal 
supply  of  phosphoric  acid  and  potash.  See  Section 


316.  Sugar  Beets.  —  This  crop  is  more  exacting  in  its 
food  requirements  than  any  other  root  crop.  Excessive 
fertility  is  not  conducive  to  a  high  content  of  sugar. 
Soils  in  good  mechanical  condition  and  medium  state 
of  fertility  usually  give  the  best  results.79  Sugar  beets 
should  not  receive  heavy  dressings  of  stable  manure, 
because  an  abnormal  growth  results.  Nitrogenous  fer- 
tilizers may  be  applied  only  in  limited  amounts,  heavier 


266  SOILS   AND   FERTILIZERS 

dressings  of  potash  and  phosphoric  acid  are  admissible. 
When  sugar  beets  follow  corn  which  has  been  manured, 
or  grain  which  has  left  the  soil  in  an  average  state  of 
fertility,  and  a  medium  dressing  of  commercial  fertilizer  is 
applied,  the  food  requirements  of  the  crop  are  well  met. 

317.  Roots.  —  Mangels    are   gross    feeders    and    re- 
move a  larger   amount  of  fertility  from  the  soil  than 
any  other  farm   crop.74     When  fed  to  stock  and  the 
manure  is  returned  to  the  soil,  they  materially  aid  in 
making   the    plant    food    more    available  for   delicate- 
feeding  crops.     Mangels  are  better  able  to  obtain  phos- 
phoric acid  than  are  turnips   and  need  the  most  help 
in  the  way  of  nitrogen.     Turnips  are  surface  feeders 
with  stronger  power  of  nitrogen  assimilation  than  the 
grains,  but  with  restricted  power  of  phosphate  assimi- 
lation.    Manures  for  turnips  should  be  phosphatic  in 
nature. 

318.  Rape  is   a   type  of  strong  feeding  plant  capa- 
ble of  obtaining  its  food  under  conditions  adverse  to 
grain  crops.      When  grown    too  frequently  upon    the 
same  soil,  it  does  not  thrive.     On  account  of  its  great 
capacity  for  obtaining   food,  it   is    a  valuable  crop  to 
use  for  green  manuring  purposes.80     Farm  manure  is 
the  most  valuable  fertilizer  for  rape. 

319.  Buckwheat   is    a    strong    feeding  crop,  and  its 
demands  for  food  are  easily  met.     On  rich  soil,  a  rank 
growth  of   straw   results,   with   poor  seed   formation. 


FOOD  REQUIREMENTS  OF  CROPS          267 

Buckwheat  is  usually  sown  upon  the  poorest  soil  of  the 
farm.  Because  it  is  a  strong  feeder  it  is  frequently 
used  as  a  manurial  crop,  being  plowed  under  while 
green  to  serve  as  food  for  weaker  feeding  crops.  On 
poor  soils  a  moderate  use  of  mineral  fertilizers  and  a 
small  amount  of  nitrogen  are  beneficial. 

320.  Cotton.  —  On  average  soils  cotton  stands  in  need 
first  of  phosphoric  acid  and  second  of  nitrogen.81     It  is 
most  able  to  obtain  potash.     Organic  nitrogen  as  cot- 
tonseed meal    and    stable   manure  appear    equally   as 
effective  as  nitric  nitrogen.     Phosphoric  acid  must  be 
applied  in  the  most  available  forms,  although  the  crop 
uses  but  little.     The  fertilizers  should  be  drilled  in  at  the 
time  of  planting.     The  use  of  gree^  manuring  crops  as 
cowpeas,  with  an  application  of  marl,  gives  beneficial  re- 
sults.    Marl,  which  is  composed  mainly  of  calcium  car- 
bonate, combines  with  the  acids  formed  from  the  decay 
of  the  vegetable  matter  and  as  a  result  the  plant  food  of 
the  soil  is  made  more  available,  which  is  beneficial  to 
both  soil  and  crop.     There  are  but  few  crops   which 
respond  so   readily  to   fertilizers   as   cotton.      It  does 
not  remove  a  large  amount  of  fertility,  but  when  not 
systematically  grown   in  a  rotation  exhausts   the   soil 
in  the  same  way  as  when  grain  is  grown  continuously. 

321.  Hops.  —  The  hop  plant  is  exacting  in  its  food 
requirements.     An  excess  of  easily  soluble  plant  food  is 
injurious,  while  a  lack  is  equally  so.     An  abundance  of 


268  SOILS    AND    FERTILIZERS 

food  in  organic  forms  is  most  essential.  Heavy  dressings 
of  farm  manures  may  be  applied.  Where  hops  are 
grown  there  is  a  tendency  to  use  all  the  manure  on 
the  hops,  while  the  rest  of  the  farm  is  left  unma- 
nured.  Very  light  applications  of  commercial  fertili- 
zers may  be  used  in  connection  with  stable  manure, 
but  such  use  should  be  made  only  after  a  preliminary 
trial  on  a  small  scale. 

322.  Hay  and  Grass  Crops.  —  Most  grass  crops  have 
shorter  roots  than  grain  crops ;  they  are  surface  feeders 
and  not  so  able  to  secure  mineral  food.      When  a  num- 
ber of  crops  have  been  removed,  the  soil  may  stand  in 
need  of  available  mineral  matter.      Farm  manures  are 
particularly  well  adapted  for  fertilizing  grass.     Applica- 
tions of  nitrogenous  manures  result  in  discouraging  the 
growth  of  clover.     Heavy  manuring  of  grass  land  has  a 
tendency  to  reduce  the  number  of  species,  and  one  kind 
is  apt  to  predominate.82     On  some  soils  ashes,  and  on 
others  lime  fertilizers,  have  been  found  very  beneficial. 
The  manuring  of  grass  must  be  varied  to  meet  the  needs 
of  different  soils.     Permanent  meadows  require  different 
manuring  from  meadow  introduced  as  an  important  crop 
in  the  rotation.     Permanent  meadows  should  receive  an 
annual  dressing  of  farm  manure  or  of  a  commercial  fer- 
tilizer containing   phosphoric  acid,   potash,  and  a  fair 
amount  of  nitrogen. 

323.  Leguminous    Crops.  —  For    leguminous    crops 
potash  and  lime  fertilizers  have  been  found  of  special 


FOOD  REQUIREMENTS  OF  CROPS          269 

value.  Analyses  of  clover  and  peas  show  large  amounts 
of  both  potash  and  lime.  In  some  cases  an  application  of 
phosphate  fertilizer  is  necessary  before  a  crop  of  clover 
can  be  secured.  Farm  manure  on  sandy  or  heavy  clay 
soils  will  materially  assist  in  the  production  of  clover. 
Sometimes  clover  fails  when  grown  too  frequently  upon 
the  same  soil,  not  because  the  soil  is  exhausted  but  be- 
cause of  the  development  in  the  soil  of  organic  products 
which  are  destructive  to  growth.  As  the  result  of  grow- 
ing leguminous  crops,  the  food  requirements  of  which 
are  inexpensive,  the  soil  is  enriched  with  nitrogen,  and 
the  phosphoric  acid  is  changed  to  available  forms. 

324.  Garden  Crops.  —  For  general  garden  purposes, 
there  should  be  a  liberal  supply  of  plant  food.  Well- 
composted  farm  manure  can  advantageously  be  ree'n- 
forced  with  commercial  fertilizers.  A  liberal  use  of 
manure  insures  not  only  the  maximum  yield,  but  crops 
of  the  best  quality.  Maturity  of  crops  also  is  influenced 
by  fertilizers. 

Voorhees89  recommends  as  a  fertilizer  for  general  gar- 
den purposes  one  containing : 


PER  CENT 

Nitrogen      

4.OO 

Phosphoric  acid    

8.00 

Potash    

IO.OO 

This  and  similar  fertilizers  can  be  applied  at  the  rate 
of  looo  pounds  per  acre.     To  meet  the  requirements 


2/O  SOILS   AND    FERTILIZERS 

of  special  crops,  as  spinach  and  cabbage,  an  additional 
dressing  of  nitrate  of  soda  may  be  used.  Asparagus 
should  preferably  be  fertilized  after  harvesting  the 
crop,  so  as  to  encourage  new  growth  and  the  storing 
up  of  reserved  building  material  in  the  roots  for  next 
year's  growth. 

For  early  maturing  garden  crops,  a  fair  but  not  ex- 
cessive amount  of  nitrogen  should  be  applied;  also  a 
liberal  supply  of  phosphates  will  be  found  advantageous. 
Some  garden  crops,  as  cucumbers,  pumpkins,  and  squash, 
thrive  best  when  their  food  is  in  organic  forms,  as  the 
humate  compounds  derived  from  farm  manures.  A 
continuous  supply  of  available  plant  food  is  thus  fur- 
nished to  the  growing  crop.  Onions  are  benefited  by 
a  generous  dressing  of  soluble  nitrogen.  Celery  also 
should  be  well  supplied  with  soluble  nitrogen  combined 
with  soluble  forms  of  mineral  food.  Tomatoes  require 
general  fertilizing ;  for  early  maturity,  nitrogen,  as 
nitrate  of  soda,  is  beneficial,  but  an  excess  should  be 
avoided ;  for  late  maturity,  farm  manures  and  com- 
mercial fertilizers  containing  less  nitrogen  may  be 
used.  For  general  garden  purposes,  a  complete  fer- 
tilizer is  preferable  to  an  amendment,  as  a  better  bal- 
anced growth  is  secured  which  favorably  affects  both 
the  yield  and  the  quality. 

325.  Fruit  Trees.  —  In  the  manuring  of  fruit  trees, 
the  first  object  is  to  produce  thrifty  trees,  as  subsequent 
fertilizing  for  fruit  will  not  give  satisfactory  results  with 


FOOD  REQUIREMENTS  OF  CROPS         2/1 

poorly  grown  and  partially  developed  trees.  In  order 
to  promote  growth,  a  liberal  supply  of  a  complete  ferti- 
lizer should  be  used,  and  the  soil  should  be  kept  in  the 
best  mechanical  condition.  When  an  orchard  is  in  full 
bearing,  there  is  as  heavy  a  draft  upon  the  soil  as  when 
a  wheat  crop  is  grown.90  To  meet  this,  farm  manures 
and  commercial  fertilizers  should  be  used  liberally. 
The  productive  period  of  an  orchard  is  materially 
lengthened  by  judicious  use  of  fertilizers.  The  quality 
of  the  fruit  is  often  adversely  affected  by  a  scant  supply 
of  plant  food.  A  quick  acting  fertilizer,  containing 
kainit,  nitrate  of  soda,  and  dissolved  phosphate  rock, 
should  be  used  in  the  spring,  followed  if  necessary  by 
a  light  dressing  of  some  manure  which  yields  up  its 
fertility  more  slowly.  An  excess  of  nitrogen,  however, 
should  be  avoided.  Stone  fruits  are  benefited  by  the 
addition  of  lime  to  the  fertilizer.  Lime  fertilizers  impart 
hardiness  to  fruit  trees. 

326.  Small  Fruits.  —  On  account  of  the  comparatively 
limited  bearing  period  of  small  fruits,  the  land  should 
be  brought  to  a  high  state  of  productiveness  and 
good  physical  condition  by  liberal  use  of  farm  manures 
previous  to  planting.  Quick  acting  fertilizers  are  the 
most  suitable  for  small  fruits.  Dressings  of  nitrate  of 
soda,  50  to  100  pounds  per  acre,  can  be  applied  early  in 
the  season  to  promote  leaf  activity.  This  should  be 
followed  by  an  application  of  a  general  fertilizer  con- 
taining about  3  per  cent  of  available  nitrogen,  8  per 


2/2  SOILS   AND   FERTILIZERS 

cent  of  phosphoric  acid,  and  10  per  cent  of  potash. 
The  amount  used  should  range  from  200  to  400  pounds 
per  acre  until  the  character  and  needs  of  the  soil  are 
determined.  It  will  often  be  found  that  large  amounts 
can  be  used  economically. 

327.  Lawns.  —  In  making  a  lawn,  a  mixture  of  six 
parts  of  bone  ash ,  two  parts  of  muriate  of  potash,  and 
one  part  of  nitrate  of  soda  can  be  applied  at  the  rate  of 
5  to  7  pounds  per  square  rod  prior  to  seeding.  A  good 
lawn  should  have  a  subsoil  that  is  fairly  retentive  of 
moisture,  one  containing  10  to  15  per  cent  of  clay  or 
a  large  amount  of  fine  silt.  Too  much  potash  and 
lime  encourage  exclusive  growth  of  clover  and  crowd- 
ing out  of  grasses.  During  the  season,  two  or  three 
applications  can  be  made  of  a  commercial  fertilizer 
containing  about  3  per  cent  of  nitrogen,  10  per  cent 
of  phosphoric  acid,  and  3  per  cent  of  potash,  at  the 
rate  of  one  pound  per  square  rod.  When  part  of  the 
nitrogen  is  in  the  form  of  nitrates  and  part  as  ammo- 
nium salts,  better  results  are  secured  than  when  the 
nitrogen  is  all  in  one  form.  It  is  also  advisable  to 
supply  the  phosphoric  acid  in  more  than  one  form. 
An  even  application  of  fertilizer  to  a  lawn  is  quite 
necessary,  otherwise  the  growth  is  "patchy."  Hard 
wood  ashes  evenly  spread  at  the  rate  of  I  to  2  pounds 
per  square  rod  and  reenforced  with  nitrate  of  soda  can 
be  used  advantageously  as  a  lawn  fertilizer. 


CHAPTER  XII 

ROTATION   OF   CROPS   AND    CONSERVATION   OF   SOIL 
FERTILITY 

328.  Object  of  Crop  Rotation.  — The  object  of  system- 
atic rotation  of  crops  is  to  conserve  the  fertility  of  the 
soil  and  at  the  same  time  to  produce  maximum  yields. 
In  order  to  accomplish  this,  the  food  requirements 
of  different  crops  must  be  met  by  good  cultivation 
and  judicious  manuring.  Rotations  must  be  planned 
according  to  the  nature  of  the  soil  and  the  system  of 
farming  that  is  to  be  followed.  For  general  grain 
farming  a  different  rotation  is  required  than  for  ex- 
clusive dairying.  Whatever  the  nature  of  farming,  the 
whole  farm  should  gradually  undergo  a  systematic  ro- 
tation. .If  the  farm  is  uneven  in  soil  texture,  different 
rotations  may  be  practiced  on  the  various  parts.  There 
is  no  way  in  which  soils  are  more  rapidly  depleted  of 
fertility  than  by  the  continued  culture  of  one  crop.  In 
exclusive  wheat  raising,  for  example,  the  losses  are  not 
confined  to  the  fertility  removed  in  the  crop,  but  other 
losses  occur  as  described  in  the  chapter  on  nitrogen. 
When  wheat  is  systematically  grown  in  alternation  with 
other  crops,  losses  of  nitrogen  are  reduced  to  the  mini- 
mum. 

T  273 


274  SOILS   AND   FERTILIZERS 

When  remunerative  crops  can  no  longer  be  produced, 
the  soil  is  said  to  be  exhausted.  Soil  exhaustion  may 
be  due  either  to  a  lack  of  plant  food,  to  bacterial 
products,  or  to  poor  physical  conditions  arising  from 
the  soil  being  temporarily  out  of  condition  because  of 
a  one-crop  system  and  poor  methods  of  cultivation. 

329.  Principles  involved  in  Crop  Rotation.  —  There 
are  a  few  fundamental  principles  with  which  all  rota- 
tions should  conform.  Briefly  stated  these  are  : 

1.  Deep-  and  shallow-rooted  crops  should  alternate. 

2.  Humus-consuming    and    humus-producing    crops 
should  alternate. 

3.  Crops  should  be  rotated  so  as  to  make  the  best 
use  of  the  preceding  crop  residue. 

4.  Crops  should  be  rotated  so  as  to  secure  nitrogen 
indirectly   from    atmospheric    sources  and   to   promote 
desirable  bacterial  activities  in  the  soil. 

5.  Crops  should  be  rotated  so  as  to  keep  the  soil  in 
the  best  mechanical  condition. 

6.  In  arid  regions,  crops  should  be  rotated  so  as  to 
make  the  best  use  of  the  soil  water. 

7.  An  even  distribution  of  farm  labor  should  be  se- 
cured by  a  rotation. 

8.  Farm   manures  and  fertilizers  should  be  used  in 
the  rotation  where  they  will  do  the  most  good. 

9.  Rotations   should  be   planned   so   as   to   produce 
fodder  for  stock,  and  so  that  every  year  there  will  be 
some  important  crop  to  be  sold. 


ROTATION    OF    CROPS 

330.  Deep-  and  Shallow-rooted  Crops.  —  When  deep- 
and  shallow-rooted  crops  alternate,  the  draft  upon  the 
surface  soil  and  subsoil  is  more  evenly  distributed  and 
the  physical  condition  of  the  soil  is  improved.     In  many 
soils,  nitrogen  and  phosphoric  acid  are  more  abundant 
in  the  surface  soil  while  potash  and  lime  predominate 
in   the   subsoil.      When    such   a    condition    exists   the 
alternating  of   deep-  and  shallow-rooted  crops  is   very 
beneficial,  because  the  surface  soil  is  gradually  enriched 
by  accumulations  of  fertility  from  the  subsoil,  deposited 
by  decay  of  the  residue  of  the  deep-rooted  crops. 

331.  Humus-consuming   and  Humus-producing  Crops. 
—  When  grain  or  hoed  crops  are  grown  continuously, 
oxidation  of  the  humus  occurs,  and  the  chemical  and 
physical  properties  of  the  soil  are  entirely  changed  by 
loss   of   the  humus.     The  rotating  of  grass  and  grain 
crops  and  the  use  of  stable  manure  serve  to  maintain 
the  humus  equilibrium.     On  some  soils  lime  may  be  re- 
quired along  with  the  humus  to  prevent  the  formation 
of   humic  acid,  and  in  such  cases  the  best  conditions 
exist  when  both  lime  and  humus  materials  are  supplied. 
Alternation  of  humus-producing  and  humus-consuming 
crops  is  one  of  the  essentials  of  a  rotation. 

332.  Crop  Residues.  —  Crop   residues   should  always 
be  placed  at  the  disposal  of  weak  feeding  crops.     After 
a   light   clover  and  timothy  sod,  wheat  or  flax  should 
be  grown  in   preference  to  barley   or  mangels.     The 


276  SOILS   AND    FERTILIZERS 

weak  feeding  crop  should  be  followed  by  a  strong 
feeding  crop,  and  then  each  is  properly  supplied  with 
food.  It  would  be  poor  economy,  on  an  average 
soil,  to  follow  clover  and  timothy  with  mangels,  then 
with  barley,  and  finally  with  flax,  because  the  flax 
would  be  placed  at  a  serious  disadvantage  following  two 
strong  feeding  crops.  If  reversed,  the  crops  would 
be  placed  in  order  of  assimilative  power,  and  the 
best  use  would  be  made  of  the  sod-crop  residue. 
When  crops  of  dissimilar  feeding  habits  follow  each 
other,  not  only  are  the  crop  residues  used  to  the  best 
advantage,  but  the  soil  is  relieved  of  excessive  demands 
on  special  elements.  For  example,  wheat  and  clover 
take  different  amounts  of  potash  and  lime  from  the 
soil.  Wheat  has  the  power  of  feeding  upon  silicates 
of  potash  which  clover  cannot  assimilate,  hence  wheat 
and  clover  in  rotation  relieve  the  soil  of  excessive 
demands  on  the  potash. 

333.  Nitrogen-consuming  and  Nitrogen-producing  Crops. 
—  It  is  possible  in  a  five-course  rotation  to  maintain  or 
even  increase  the  nitrogen  of  the  soil  without  the  use 
of  nitrogenous  manures.  In  Section  145  an  example 
is  given  of  a  rotation  which  has  left  the  soil  with  a 
better  supply  of  nitrogen  than  at  the  beginning. 
When  a  soil  produces  a  good  clover  crop  once  in 
five  years,  and  stable  manure  is  used  once  during 
that  time,  the  soil  nitrogen  is  not  decreased.  Not  only 
is  nitrification  influenced  by  cultivation  and  crop  rota- 


ROTATION    OF    CROPS 

tion,  but  other  bacterial  changes  are  also  affected.  The 
entire  bacterial  flora  of  a  soil  may  be  changed  by 
modifications  of  systems  of  cultivation,  cropping,  and 
manuring.  By  means  of  rotating  nitrogen-producing 
and  nitrogen -consuming  crops,  grain  can  be  sold  from 
the  farm  without  purchasing  nitrogenous  manures. 
Conservation  of  the  nitrogen  and  humus  of  the  soil 
is  one  of  the  most  important  points  to  consider  in  the 
rotation  of  crops. 

334.  Influence  of  Rotation  upon  the  Mechanical  Con- 
dition of  Soils.  —  With   different   kinds   of   crops   the 
mechanical  condition  of  soils  is  constantly  undergoing 
change.     Grain   crops   and   hoed   crops  tend  to  make 
the  soil  open  in  texture.     Grass  crops  have  the  opposite 
effect.     All  soils  should   undergo  periodic  compacting 
and  loosening.     Some   require  more  of  one  treatment 
than   of   the   other.     In   a   rotation   the   action  of  the 
crop  upon  the  mechanical  condition  of  the  soil  should 
be   considered,   otherwise  the  soil   may   get  into  poor 
condition  to  retain  water  or  become  so  loose  that  heavy 
losses   occur  through   wind    storms.     Sandy   soils   are 
improved  by  methods  of  cropping  which  compact  the 
soil,  while  heavy  clays  require  the  opposite  treatment. 
The   rotation  should   be   made   to   conform  to  the  re- 
quirement of  the  soil. 

335.  Economic  Use    of    Soil    Water.  — The    rotation 
should  not  be  of  such  a  nature  as  to  make  excessive 


2/8  SOILS   AND   FERTILIZERS 

demands  upon  the  soil  water.  For  example,  after  a 
grain  crop  has  been  produced,  it  is  best  in  regions  of 
scant  rainfall  to  plow  the  land  and  get  it  into  condi- 
tion to  conserve  the  water  for  the  next  year's  crop, 
rather  than  to  attempt  to  raise  a  catch  crop  the  same 
year.  During  years  of  heavy  rainfall  catch  crops  may 
be  grown  for  green  manure  to  increase  the  humus  con- 
tent of  the  soil.  Crops  removing  excessive  amounts 
of  water  should  not  be  grown  too  frequently.  Sim- 
flowers,  for  example,  remove  twenty  times  more  water 
than  grain  crops,  and  cabbage  removes  more  water 
than  many  other  crops.  With  a  good  rotation  and 
systematic  cultivation  a  water  balance  may  be  carried 
in  the  soil  from  one  year  to  the  next,  so  that  crops 
will  be  supplied  in  times  of  drought. 

336.  Rotation   and   Farm   Labor.  —  The   rotation   of 
crops   should   be   so    planned    that    there   is   an   even 
distribution  of  farm  labor.     The  importance  of  this  is 
so   plain   that   its   discussion    seems    unnecessary.     It 
is   one   of   the   most   important  points  to  consider  in 
economic  farming,  and  should  not  be  lost  sight  of  in 
planning  rotations. 

337.  Economic    Use    of     Manures.  —  Farm    manure 
should  be  applied  to  those  crops  which  experience  has 
shown  to  be  the  most  benefited  by  its  use.     At  least 
once   during   a   five   years'   rotation   the   land    should 
receive   a   dressing   of   stable  or  some   other   manure. 


ROTATION    OF    CROPS 


2/9 


When  commercial  fertilizers  are  used,  they  should  be 
applied  to  the  crops  which  need  the  most  help  in 
obtaining  food.  With  the  growing  of  clover  and  the 
use  of  farm  manures,  the  minimum  amount  of  com- 


FlG.  46.    A  Wheat  Field.     This  crop  was  grown  on  land  where  farm  manure 
was  used  and  a  rotation  of  crops  practiced.     Ayer,  Photographer. 

mercial  fertilizer  is  required  for  general  crop  production. 
It  is  more  economical  to  reenforce  the  farm  manures 
with  fertilizers  especially  adapted  to  the  soil  and  crop 
than  to  purchase  complete  fertilizers  for  all  crops. 

338.   Salable  Crops.  —  In  all  farming,  something  must 
be  sold   from  the  farm.     It  should  be  the  aim  to  sell 


28O  SOILS   AND    FERTILIZERS 

products  which  remove  the  least  fertility,  or  if  those 
are  sold  which  remove  large  amounts,  to  return  in 
cheaper  forms  the  fertility  sold.  In  a  good  rotation 
it  is  the  plan  to  have  at  least  one  salable  crop  each 
year.  The  whole  farm  need  not  undergo  the  same 
rotation  at  the  same  time,  and  the  rotation  may  be 
subject  to  minor  changes,  as  circumstances  require. 
To  illustrate,  wheat  and  flax  occupy  about  the  same 
position  in  a  rotation.  If  at  seeding  time  the  indica- 
tions are  that  wheat  will  be  a  poor  paying  crop  and 
flax  command  a  high  price,  flax  should  be  sown.  The 
rotation  should  be  such  that  one  of  two  or  three  crops 
may  be  grown  as  circumstances  require.  A  rotation 
should  be  reasonably  flexible. 

339.  Rotation  Advantageous  in  Other  Ways.  —  A  good 
rotation  will  be  found  advantageous  in  other  ways  than 
those  mentioned.  With  one  line  of  cropping,  land  be- 
comes foul  with  weeds  and  insects  which  do  not  thrive 
when  crops  are  rotated.  Frequently  the  rotation  must  be 
planned  so  as  to  reclaim  the  land  from  weeds  and  rav- 
ages caused  by  insect  pests.  Many  insects  are  capable 
of  living  only  on  a  special  crop  ;  when  this  crop  is  grown 
continuously  on  the  same  land  the  best  conditions  for  in- 
sect ravages  exist,  and  relief  is  secured  only  by  rotation 
of  crops.  Fungous  diseases  also  are  most  liable  to  occur 
on  soils  which  produce  annually  the  same  crop,  as  the 
conditions  are  favorable  for  the  propagation  and  hiber- 
nating of  the  disease-producing  spores. 


ROTATION   OF    CROPS  28 1 

340.  Long-   and   Short-course  Rotations.  —  Rotations 
vary  in  length  from  2  to  17  years.     Long-course  rota- 
tions' are   more   generally   followed   in    European  and 
other  of  the  older  countries.    The  length  of  the  rotation 
can  be  determined  only  by  the  conditions   existing  in 
different  localities.     As  a  general  rule,  long-course  rota- 
tions should  be  attempted  mainly  on  large  farms  and  after 
a  careful  study  of  all  of  the  conditions  relating  to  the 
system  of  farming  that  it  is  desired  to  follow.    For  north- 
ern latitudes  a  rotation  of  four  or  five  years  gives  excel- 
lent results.     In  some  localities   three-course  rotations 
are  the  most  desirable. 

A  rotation  that  is  suitable  for  one  locality  or  kind  of 
farming  may  be  unsuitable  for  other  localities  and  con- 
ditions. Because  of  variations  in  soil,  climate,  and  rain- 
fall, no  definite  standard  rotation  can  be  proposed  that 
will  be  applicable  to  all  cases. 

341.  Example  of  Rotation.  —  In  dealing  with  the  sub- 
ject of  rotations  it  is  best  to  take  actual  problems  as 
they  present  themselves  and  plan  rotations  that  will 
best  meet  all  of  the  conditions.     For  example,  a  farm 
of  1 60  acres  is  to  be  rotated  with  the  main  object  of 
producing  fodder  for  live  stock,  and  a  small  amount  of 
grain  for  sale.    To  meet  these  requirements  the  rotation 
outlined  on  pages  282  and  283  is  suggested.83 

The  farm  is  divided  into  eight  fields  of  20  acres  each; 
seven  fields  are  brought  under  the  rotation,  while  one 
field  is  left  free  for  miscellaneous  purposes.  Each  year 


SOILS   AND    FERTILIZERS 


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284  SOILS   AND    FERTILIZERS 

there  are  produced  20  acres  of  corn,  20  acres  of  timothy 
and  clover  hay,  10  acres  each  of  wheat  and  flax,  20  acres 
of  barley,  and  5  acres  each  of  corn  fodder,  rye,  peas, 
and  potatoes,  while  20  acres  are  reserved  for  pasture. 
The  main  income  is  derived  from  the  sale  of  live  stock 
and  dairy  products. 

Problems  on  Rotation 

1.  Plan  a  rotation  for  general  farming   (160   acres),  using  the 
following  crops :  clover,  timothy,  barley,  oats,  potatoes,  and  corn. 
The  soil  is  in  an  average  state  of  fertility.      Twenty-five  head  of 
stock  are  kept. 

2.  Plan  a  three-course  rotation  for  a  sandy  soil,  the  main  object 
being  potato  culture. 

3.  Plan  a  seven-year  rotation  for  grain  farming,  using  manure 
and  a  commercial  fertilizer  once  during  the  rotation.     The  soil  is 
a  clay  loam  in  a  good  state  of  fertility. 

4.  Plan  a  rotation  for  general  farming  on  a  sandy  loam. 

5.  How  would  you  proceed  to  bring  an  old  grain  farm  from  a 
low  to  a  high  state  of  productiveness  ?     Begin  with  the  feeding  of 
the  stock. 

6.  Using  commercial  and  special  purpose   manures,  how  would 
you  proceed  to  raise  wheat,  potatoes,  and  hay  in  a  suitable  rotation 
and  continuously? 

7.  Plan  a  rotation  for  a  northern  latitude,  where  corn  cannot  be 
grown,  except  for  fodder,  and  where  clover  and   timothy  fail  to 
do   well ;  wheat  and  all  small  grains  thrive,  also   millet,  bromus 
inermis,  rape,  and  some  of  the  root  crops.     The  soil  is  a  clay  loam, 
resting  on  a  marl  subsoil.     Manure  is  very  slow  in  decomposing. 
The  rotation  should  be  suited  to  general  farming,  wheat  or  flax 
being  the  important  market  crop. 

8.  Plan  for  a  southern  farm  a  rotation  in  which  cotton  forms  an 
important  part. 


CONSERVATION    OF    FERTILITY  285 

9.  Plan  a  rotation  for  a  market  milk  farm  of  90  acres.  One  hun- 
dred head  of  stock  are  kept  and  mostly  mill  feed  purchased. 
Soiling  crops  are  to  be  provided ;  corn  silage  and  clover  are  the 
main  coarse  fodders. 


CONSERVATION  OF  FERTILITY 

342.  Manures  Necessary  for  Conservation  of  Fertility. 
—  In  order  to  conserve  the  fertility  of 'the  soil,  not  only 
must  a  systematic  rotation  be  practiced,  but  a  proper 
use  must  be  made  of  the  crops  produced.     When  crops 
are  sold  from  the  farm  and  no  restoration  is  made,  soils 
are  gradually  depleted  of  their  fertility.     No  soil  has 
ever  been  found  that  will  continue  to  produce  crops 
without  the  use  of  manures.     Many  prairie  soils  give 
large   yields  for   long  periods   without  manuring,  but 
they  are  never  able  to  compete  in  productiveness  with 
similar  soils  that  have  been  systematically  cropped  and 
manured.     With  a  fertile  soil  the  decline  in  fertility  is 
so  gradual  that  it  is  not  observed  unless  careful  records 
are  kept  of  the  yields  from  year  to  year. 

343.  Use  of  Crops.  —  The  use  made  of  crops  whether 
as  food  for  stock  or  sold  directly  from  the  farm  de- 
termines the  future  crop-producing  power  of  the  soil. 
With  different  systems  of  farming  different  uses  are 
made  of  crops.     When  exclusive  grain  farming  is  fol- 
lowed there  is  no  restoration  of  fertility,  while  in  the 
case  of  stock  farming,  the  manure  produced  contains 
fertility  in  proportion  to  the  food  consumed.     If  good 


286  SOILS    AND    FERTILIZERS 

care  is  taken  of  the  manure,  and  in  place  of  the  grains 
sold  mill  products  are  purchased  and  fed,  there  is  no 
loss  but  often  a  gain  of  fertility.  Between  these  two 
extremes,  exclusive  grain  farming  and  stock  farming, 
many  different  systems  are  practiced  which  remove 
from  the  soil  various  amounts  of  fertility. 

344.  Two  Systems  of  Farming  Compared.  —  Losses 
of  fertility  from  farms  are  determined  by  the  products 
sold,  the  care  of  the  manure,  and  the  fertility  in  the 
materials  purchased  and  used  on  the  farm.  If  an  ac- 
count were  kept  of  the  income  and  outgo  of  the  fertility 
it  would  be  found  that  with  some  systems  the  soil 
is  gaining,  while  with  others  a  rapid  decline  is  occur- 
ring. In  studying  the  income  and  outgo  of  fertility,  it 
is  necessary  to  calculate  the  amounts  of  the  three  prin- 
cipal elements,  nitrogen,  phosphoric  acid,  and  potash  in 
the  crops  and  other  products  sold.  For  making  these 
calculations,  tables  are  given  in  Sections  185  and  307. 
In  the  handling  of  manure  it  is  impossible  to  prevent 
losses,  but  it  is  possible  to  reduce  them  to  very  small 
amounts.  Hence  in  the  calculations,  a  loss  of  3  per 
cent  is  allowed  for  mechanical  waste  and  for  uneven 
distribution  of  the  manure;  that  is,  in  addition  to  the 
fertility  sold  from  the  farm  a  mechanical  loss  of  3  per 
cent  is  allowed  for  all  crops  raised  and  consumed  as 
food  by  stock. 

On  one  farm  the  crops  raised  and  sold  are :  flax  40 
acres,  wheat  50  acres,  oats  20  acres,  barley  50  acres 


CONSERVATION    OF   FERTILITY 


287 


No  stock  is  kept,  the  straw  is  burned,  and  the  ashes 
are  wasted.  In  addition  to  the  nitrogen  removed  in 
the  crops  other  losses  must  be  considered.  Experiments 
show  that  when  exclusive  grain  farming  is  practiced, 
for  every  pound  of  nitrogen  removed  in  the  crop,  4 
pounds  are  lost  from  the  soil  in  other  ways.  This  would 
make  the  total  loss  of  nitrogen  over  28,500  pounds, 
or  177  pounds  per  acre,  which  large  as  it  may  seem 
is  the  actual  loss  from  the  soil  when  grain  only  is  raised 
and  it  is  sold.  Experiments  at  the  Minnesota  Experi- 
ment Station  with  a  soil  that  had  been  cultivated  40 
years,  showed  the  annual  loss  per  acre  of  nitrogen  in 
exclusive  wheat  raising  to  be  25  pounds  through  the 
crop  and  146  pounds  due  to  oxidation  of  the  nitroge- 
nous humus  of  the  soil.9 

EXCLUSIVE  GRAIN  FARMING 
Sold  from  the  Farm 


NITROGEN- 
POUNDS 

PHOSPHORIC 
ACID 
POUNDS 

POTASH 
POUNDS 

Flax,  40  acres    

l6oo 

600 

800 

Flax  straw     

600 

1  2O 

•72O 

\Vheat,  50  acres      

I2CO 

62; 

•ICO 

\Vheat  straw      

COO 

•375 

1400 

Oats,  20  acres    

7OO 

24.O 

2OO 

Oat  straw      

•7  (JO 

1  2O 

7OO 

Barley,  50  acres      

I4OO 

7  co 

4OO 

Barley  straw       

6oO 

2  Co 

I  COO 

Total      

60  CO 

308o 

C.67O 

When  exclusive  grain  farming  was  followed,  the  annual 
losses  of  fertility  from  this  farm  of  160  acres  were  28,500 


288 


SOILS   AND   FERTILIZERS 


pounds  of  nitrogen,  3000  pounds  of  phosphoric  acid, 
and  5500  pounds  of  potash. 

On  a  similar  farm  of  160  acres  the  crops  are  rotated 
as  described  in  Section  341.  The  amounts  of  fertility 
in  the  crops  raised  and  consumed  as  fodder,  in  the 
products  sold,  and  in  the  food  and  fuel  purchased,  are 
given  in  the  following  table : 

STOCK  FARMING 
Sold  from  the  Farm 


NITROGEN 
POUNDS 

PHOSPHORIC 
ACID 
POUNDS 

POTASH 

POUNDS 

Butter  5000  pounds  ..... 

5" 

c 

Young  cattle,  10  head     .... 
Hogs,  20  of  250  pounds  each  .     . 
Steers,  2    

2OO 
100 

48 

IQO 
40 
•*8 

16 

10 

\Vheat,  10  acres     

2CO 

I2C 

7O 

Flax   10  acres    

•3QO 

I  CO 

IQO 

Rye,  10  acres     

281; 

128 

8; 

Total     .          

1278 

676   • 

^80 

Raised  and  Consumed  on  the  Farm 


Clover,  20  tons  

2  7O 

6OO 

Timothy  20  tons   • 

600 

1  80 

8OO 

Corn,  20  acres   

I  COO 

"?OO 

800 

Com  fodder,  i  acre     

7C 

1  e 

60 

Mangels,  2  acres    

I  CO 

7O 

•*oo 

Potatoes   i  acre     

AO 

2O 

7C 

Straw  4.0  tons   

AOO 

2OO 

IOOO 

Peas,  5  acres      

8c 

2OO 

Oats  20  acres         

7OO 

24O 

2OO 

Barley,  20  acres  with  straw      .     . 

800 

4OO 

760 

Total      

4.26? 

1780 

47QC 

Mechanical  loss  of  food  consumed, 
3  per  cent  

128 

C7 

144 

CONSERVATION    OF    FERTILITY 


289 


Food  and  Fuel  Purchased 


NITROGEN 
POUNDS 

PHOSPHORIC 
ACID 
POUNDS 

POTASH 
POUNDS 

Bran,  5  tons       

27C 

260 

I  CO 

Shorts,  5  tons    

2  SO 

I  CO 

IOO 

Oil  meal,  i  ton  

IOO 

•1C 

2C. 

Hard  wood  ashes  

2C. 

IOO 

Total     

62? 

4.7O 

•37  c 

Mechanical  loss  of  material  pur- 
chased, 3  per  cent  

IQ 

IO 

Sold  from  farm       

1278 

676 

l8o 

Loss  of  food  consumed,  etc.     .     . 

128 

53 

144 

Total     

1425 

7/1-5 

t-\A 

Food  and  fuel  purchased     .     .     . 
Balance  lost  from  farm  .... 

625 
800 

47° 
273 

375 
:59 

The  manure  produced  and  used  on  this  farm  results 
in  larger  crop  yields  than  is  the  case  with  exclusive  grain 
culture.  The  nitrogen  gained  by  the  clover  and  peas 
more  than  balances  the  loss  of  nitrogen  in  other  crops. 
Experiments  show  that-  a  rotation  similar  to  this  caused 
an  increase  in  soil  nitrogen.18  Manure,  meadow,  and 
pasture  all  tend  to  increase  the  soil's  humus  and  ni- 
trogen. The  losses  of  phosphoric  acid  and  potash 
are  very  small,  averaging  about  a  pound  per  acre  of 
each.  The  manure  on  this  farm  is  continually  bringing 
into  activity  the  inert  plant  food  of  the  soil  so  that 
every  year  there  is  a  larger  amount  of  more  active 
plant  food,  which  results  in  producing  larger  yields 
per  acre. 


2QO  SOILS    AND    FERTILIZERS 

The  method  of  farming  has  a  marked  effect  upon 
crop  yields.  The  average  yield  of  wheat  in  those 
counties  in  Minnesota  where  live  stock  is  kept  and 
crops  are  rotated,  is  over  10  bushels  per  acre  greater 
than  in  similar  counties  where  exclusive  grain  farming 
is  followed. 

Problems 

Calculate  the  income  and  outgo  of  fertility  from  the  following 
farms: 

1.  Sold  from  the  farm:  wheat  40  acres,  oats  40  acres,  barley  40 
acres,  rye  20  acres,  flax  10  acres.     The  straw  is  burned  and  no 
manures  are  used. 

2.  Sold  from  the  farm :  wheat  20  acres,  barley  20  acres,  flax  5 
acres,  1000  pounds  of  butter,  10  hogs,  and  10  steers.     Purchased  : 
bran  3  tons,  shorts  2  tons,  oil  meal  i  ton.     Crops  produced  and  fed 
on  farm :  clover  and  timothy  hay  40  tons,  corn    fodder  3  acres, 
corn  10  acres,  oats  and  peas  10  acres,  roots   i   acre,  millet  I  acre, 
and  barley  5  acres. 

3.  Sold  from  the  farm  :  wheat  10  acres,  sugar  beets  5  acres,  milk 
100,000  pounds,  butter  500  pounds,  20  pigs,  6  head  of  young  stock, 
2  acres  of  potatoes.     Purchased  :  5  tons  of  bran,  2  tons  of  oil  meal, 
i  ton  of  cottonseed  meal,  1 5  cords  of  wood,  i  ton  of  acid  phosphate, 
1000  pounds  of  potassium  sulphate,  and   500  pounds  of  sodium 
nitrate.     Raised  and  consumed  on  the  farm:  corn  fodder  15  acres, 
mangels  i  acre,  peas  and  oats  5  acres,  clover  20  tons,  timothy  10 
tons,  straw  from  grain  sold,  oats  ro  acres,  corn  20  acres. 

4.  Calculate  the  income  and  outgo  of  fertility  from  your  own 
farm. 


CHAPTER  XIII 
PREPARATION  OF  SOILS  FOR  CROPS 

345.  Importance  of  Good  Physical  Condition  of  Seed 
Bed.  —  But  few  soils  are  in  suitable  condition  for  seed- 
ing without  further  preparation  than  simply  plowing  the 
land.     If  the  plowing  is  poorly  done,  a  good  seed  bed 
cannot  be  made.     The  depth  of  plowing  is  of  prime 
importance  and  is  determined  largely  by  the  kind  of 
soil,  as  sand,  clay,  or  loam.     (See  Section  35.)    The 
condition  of  the  seed  bed  is  influenced  not  only  by  the 
depth  of  plowing  but  by  its  nature  as  the  way  in  which 
the  furrow  slice  is  left.     The  treatment  after  plowing,  as 
disking,  harrowing,  cultivating,  and  light  rolling,  must  be 
determined  largely  by  the  character  of  the  soil.     Too 
frequently  the  preparation  of  the  soil  is  not  given  suf- 
ficient attention  and  the  crop  suffers  because  of  a  poorly 
prepared  seed  bed.     Low  yields  are  more  generally  due 
to  poor  physical  condition  of  the  soil  than  to  any  other 
factor.      Without  the  requisite  cultivation  the  natural 
fertility  is  not  used  to  the  best  advantage. 

346.  Influence  of  Methods  of  Plowing  upon  the  Condition 
of  the  Seed  Bed.  —  A  poor  seed  bed  is  sometimes  /due  to 
complete  inversion  of  the  furrow  slice  and  the  soil  not 
being  sufficiently  pulverized.     If  a  heavy  sod  has  simply 

291 


292 


SOILS   AND    FERTILIZERS 


been  inverted,  subsequent  harrowing  and  cultivation  fail 
to  pulverize  and  loosen  the  tough  sod  in  the  lower  part 
of  the  furrow  slice.  A  good  seed  bed  cannot  be  made 
upon  such  a  foundation.  When  the  land  is  plowed  so 
the  furrow  slice  is  left  at  an  angle  of  30°  to  45°,  the  sur- 


FlG.  47.    Complete  Inversion  of  the  Furrow  Slice  (after  Roberts) .    A  poor  way 
of  plowing  sod  land. 

face  is  corrugated  and  all  vegetation  is  buried  in  loose 
soil.  When  land  that  has  been  plowed  in  this  way  is 
cultivated  and  harrowed,  a  better  seed  bed  is  formed 
than  is  possible  on  a  completely  inverted  furrow  slice. 

The  plowing  should  thoroughly  pulverize  the  soil, 
completely  bury  all  surface  vegetation,  and  leave  the 
land  hi  a  corrugated  condition  with  the  furrow  slice  at 


PREPARATION   OF   SOILS   FOR   CROPS 


293 


an  angle  but  firmly  connected  with  the  subsoil.  There 
should  be  as  thorough  disintegration  of  the  soil  as  pos- 
sible, and  this  can  best  be  accomplished  by  the  use  of 
a  plow  with  a  bold  rather  than  too  flat  a  moldboard. 

J 


FIG.  48.  The  Furrows  standing  nearly  edgewise  (after  Roberts).  A  good 
way  to  leave  fall  plowed  land  to  undergo  weathering  during  the  winter,  to 
be  followed  by  thorough  cultivation  in  the  spring. 

Roberts  states  that  only  about  10  per  cent  of  the  energy 
required  for  plowing  is  used  by  the  friction  of  the  mold- 
board:  "about  35  per  cent  of  the  power  necessary  to 
plow  is  used  by  the  friction  due  to  the  weight  of  the 
plow,  and  55  per  cent  by  severing  the  furrow  slice  and 
the  friction  of  the  land  slide."  Hence  in  the  prepara- 
tion of  the  seed  bed,  it  is  economy  to  secure  as  much 
pulverization  of  the  soil  by  the  action  of  the  plow  as 
possible  rather  than  to  leave  too  much  for  subsequent 
treatment.  The  plow  is  the  most  economical  implement 
for  pulverizing  the  land. 


294 


SOILS   AND   FERTILIZERS 


347.  Influence  of  Moisture  Content  of  the  Soil  at  the 
Time  of  Plowing.  —  The  condition  of  the  soil,  particu- 
larly its  moisture  content,  at  the  time  of  plowing,  has 
much  to  do  with  the  formation  of  a  good  seed  bed.  If 
soils  are  too  dry  when  plowed,  they  fail  to  pulverize,  and 


FlG.  49.     Ideal  Plowing  (after  Roberts).     The  land  left  in  a  formed,  pulverized 
condition  and  all  the  sods  turned  under. 

then  disking,  harrowing,  and  in  some  cases  light  rolling, 
which  make  additional  expense,  must  be  resorted  to 
in  order  to  produce  a  fine,  mediumly  compact,  and  well- 
pulverized  seed  bed.  If  clay  soils  are  plowed  when  too 
wet,  the  pores  of  the  subsoil  become  clogged,  a  condi- 
tion known  as  puddling  takes  place,  and  the  furrow 
slice  dries  and  forms  hard  lumps  and  clods.  The  con- 
dition in  which  the  soil  is  left  after  plowing,  particularly 
in  the  case  of  clay  soils,  has  much  to  do  with  the  char- 
acter of  the  seed  bed  and  the  subsequent  yield  of  the 
crop.  At  the  Oklahoma  Station,  winter  wheat  land 
plowed  in  July  was  moist  and  mellow,  while  that  plowed 


PREPARATION    OF    SOILS    FOR    CROPS  295 

in  September  was  dry  and  lumpy ;  the  early  plowed 
mellow  land  gave  a  yield  of  31.3  bushels  per  acre  and 
the  late  plowed  lumpy  land  produced  only  13.3  bushels. 

348.  Influence  upon  the  Seed  Bed  of  Pulverizing  and 
Fining  the  Soil.  —  If  the  land  is  lumpy  and  the  lower 
stratum  of  the  seed  bed  is  not  pulverized  and  firmed,  the 
soil  water  is  readily  lost  by  percolation,  evaporation  takes 
place  rapidly,  and  the  crops  are  poorly  fed  because  the 
roots  are  unable  to  penetrate  the  hard  lumps  and  secure 
plant  food.     If  a  soil  is  inclined  to  be  lumpy,  the  cul- 
tivation, including  the  plowing,  should  be  carried  on 
largely  with  the  view  of  thorough  pulverization.     When 
a  seed  bed  is  well  prepared,  the  soil  warms  up  more 
readily;     the    loosening    and    pulverizing    enable    the 
heat  of  the  sun's  rays  to  more  readily  penetrate  the 
soil   and  bring   it   into  good  condition   for   promoting 
growth. 

349.  Aeration  of  Seed  Bed  Necessary.  —  Crop  roots 
require  air  for  functional  purposes.     In  sand  and  loam 
the   air   spaces   make   up   half   or   more   of   the   total 
volume.     It  is  not  necessary  to  cultivate  such  soil  with 
the  view  of  increasing  the  air  spaces,  but  with  compact 
soils,  as  heavy  clays,  plowing  should  result  in  aeration 
of  the  soil  and  an  increase  in  the  number  of  air  spaces, 
as  the  air  of  the  soil  takes  an  important  part  in  render- 
ing plant  food  available.     (See  Section  59.)     If  soils  are 
plowed  when  too  wet,  they  are  not  sufficiently  aerated. 


296  SOILS    AND    FERTILIZERS 

The  amount  and  kind  of  cultivation  to  secure  the  venti- 
lation or  aeration  necessary  for  crop  production  must 
be  regulated  according  to  the  character  of  the  soil,  as 
sand,  clay,  or  loam,  and  the  climatic  conditions.  The 
cultivation  which  is  given  soils  for  moisture  conserva- 
tion also  secures  the  proper  aeration. 

In  discussing  the  importance  of  a  mellow  seed  bed, 
King  says  ; 15  "  When  a  mellow,  open  seed  bed  has  been 
prepared,  and  its  temperature  has  been  raised  to  the 
proper  point,  should  a  rain  fall  upon  it,  that  water  will 
tend  to  pass  through  its  wide  pores  quickly  to  the 
deeper  soil,  and  without  leaching  it  as  badly  as  would 
be  the  case  were  the  soil  more  compact ;  so  that  in 
the  early  season  when  there  is  an  overabundance  of 
moisture,  it  is  best,  for  warmth,  for  aeration,  and  to 
lessen  loss  of  fertility  by  percolation,  to  have  a  mellow 
seed  bed." 

350.  Preparation  of  Seed  Bed  without  Plowing.  — 
Loam  soils  which  have  been  subjected  to  a  systematic 
rotation  of  crops  ending  with  corn,  need  not  be  plowed, 
but  the  seed  bed  for  the  succeeding  grain  crop  can 
be  prepared  simply  by  disking  the  corn  land.  Surface 
tillage  of  the  corn  crop  has  sufficiently  loosened  and 
aerated  the  soil  and  has  caused  an  accumulation  of 
available  plant  food  near  the  surface  which  would  be 
buried  and  be  less  available  to  the  crop  if  the  land  were 
plowed  too  deeply.  On  heavy  clay  lands  this  method 
of  preparing  the  seed  bed  is  not  advisable ;  but  on  the 


PREPARATION   OF    SOILS   FOR   CROPS  297 

silt  soils  of  the  Northwest  it  has  given  excellent  results 
and  is  beneficial  in  promoting  crop  growth. 

351.  Mixing  of  Subsoil  with  Seed  Bed.  —  Some  soils 
are  improved  by  deep  plowing  and  mixing  the  surface 
and   subsoils   to   form   the   seed   bed.     Such  soils  are 
usually  acid  in  character  and  contain  a  large  amount 
of   organic   matter,  in  which   case   the  mixing  of  the 
surface  and  subsoils  improves  both  the  physical   and 
chemical  properties.     With  sandy  soils  the  mixing  of 
the  surface  soil  with  the  subsoil  is  not  advantageous,  as 
it  dilutes  the  stores  of  plant  food  which  are  greater  in 
the  surface  soil;  then,  too,  the  physical  properties  of 
the  soil  are  not  improved.      Combining  the  surface  and 
subsoils  in  the  case   of   heavy  clays   should   be   done 
gradually  and  at  ( each  period  in  the  rotation  after  an 
application  of  farm  manure.     In  the  cultivation  of  clay 
soils  it  should  be  the  aim  to  secure  a  deep  layer  of 
thoroughly  pulverized,  aerated,  and  fertilized  soil.     In 
the  preparation  of  the  seed  bed,  the  character  and  con- 
dition of  the  subsoil  is  equally  as  important  as  of  the 
surface  soil. 

352.  Cultivation  to  Destroy  Weeds.  —  One  of  the  chief 
objects  of  cultivation  is  to  destroy  weeds,  and  for  this 
purpose  it  should   be  given  early  in  the   year  before 
the  weeds  become  firmly  established.     Weeds  are  most 
easily  destroyed  at  the  time  of  germination  and  before 
the  leaves  appear  above  ground.     The  plow  should  be 


298  SOILS   AND   FERTILIZERS 

relied  upon  largely  for  the  destruction  of  deep-rooted 
perennial  weeds,  while  the  cultivator  is  effectual  for 
the  destruction  of  annuals.  When  weeds  are  plowed 
under  or  destroyed  by  cultivation  they  serve  as  a  green 
manurial  crop,  adding  vegetable  matter  and  humus  to 
the  soil  and  thus  improving  its  condition  instead  of 
reducing  the  yield  of  crops  by  appropriating  fertility, 
as  they  do  if  allowed  to  grow  and  mature.  Cultivation 
which  secures  aeration  of  the  soil  and  conservation  of 
the  soil  moisture  is  also  effectual  for  the  destruction 
of  weeds. 

353.   Influence  of  Cultivation  upon  Bacterial  Action.  — 

Cultivation  has  a  marked  influence  upon  bacterial  ac- 
tion. Some  of  the  soil  organisms,  as  the  nitrifying 
organisms  (see  Section  150),  require  oxygen  for  their 
existence,  hence  cultivation  which  increases  the  sup- 
ply of  oxygen  in  the  soil  increases  the  activity  of  such 
organisms.  In  the  absence  of  air,  anaerobic  fermenta- 
tion occurs,  and  such  fermentation  is  unfavorable  to 
crop  growth.  When  acid  peaty  soils  are  aerated  bac- 
terial action  is  induced  which  results  in  more  rapid 
decay  and  a  lowering  of  the  per  cent  of  total  organic 
matter,  including  the  deleterious  organic  acids.  Neu- 
tralizing the  organic  acids  of  soils  by  applications  of 
lime  and  wood  ashes  hastens  bacterial  action,  and  during 
the  process  of  nitrification  this  is  not  alone  confined 
to  the  nitrogenous  compounds  of  the  soil,  as  the  nitri- 
fying organisms  require  phosphates  as  food  and  these 


PREPARATION   OF   SOILS   FOR   CROPS  299 

are  left  after  nitrification  in  a  more  available  condition. 
The  mineral  as  well  as  the  organic  matter  of  the  soil 
is  subject  to  the  action  of  micro-organisms,  and  the 
cultivation  which  the  soil  receives  can  be  made  either 
to  accelerate  or  to  retard  this  action.  Many  of  the 
chemical  changes  which  take  place  in  the  soil  result- 
ing in  the  liberation  of  plant  food  are  induced  by  aerobic 
organisms,  hence  the  importance  of  thorough  cultiva- 
tion to  induce  bacterial  action.  Each  type  of  soil  has 
its  own  characteristic  microscopic  flora,  which  can  be 
either  favorably  or  unfavorably  influenced  by  cultivation. 

354.  Cultivation  for  Special  Crops.  —  While  the  gen- 
eral principles  of  cultivation  apply  to  all  crops,  the  ex- 
tent to  which  loosening  or  compacting  should  be  carried 
must  be  determined  by  the  character  of  the  soil  and  the 
crop  that  is  to  be  produced.  Methods  of  cultivation 
must  be  varied  to  meet  the  requirements  of  different 
soils  and  different  crops.  The  physical  condition  of 
the  soil  for  general  farm  crops  is  discussed  in  Chapters 
I  and  XL  For  the  production  of  a  special  crop,  the 
cultivation  must  be  adapted  to  the  specific  needs  as 
to  manner  of  growth,  kind  of  food  needed,  physical 
condition  of  the  soil,  temperature,  and  moisture.  A 
knowledge  of  these  requirements  can  be  obtained  only 
by  experimental  methods.  The  cultivation  of  a  new 
crop  should  not  be  attempted  on  a  large  scale  without 
a  preliminary  study  of  the  crop.  The  production  of 
sugar  beets  for  the  manufacture  of  sugar,  of  flax  for 


3OO  SOILS   AND   FERTILIZERS 

fine  fiber,  or  of  tobacco  under  shade  requires  a  high 
degree  of  both  knowledge  and  skill.  For  the  pro- 
duction of  special  crops  the  preparation  of  the  seed 
bed  and  the  subsequent  cultivation  are  matters  of  prime 
importance,  and  should  receive  careful  consideration  on 
the  part  of  the  cultivator.  Many  times  agricultural 
industries  undertaken  in  new  countries  have  failed 
because  the  cultivation  of  the  special  crop  used  in  the 
industry  has  not  been  successfully  accomplished  on 
account  of  lack  of  knowledge  of  the  cultural  methods 
necessary. 

355.  Cultivation  to  prevent  Washing  and  Gullying  of 
Lands.  —  In  regions  of  heavy  rainfall,  rolling  land  of 
clay  texture  often  becomes  gullied  by  the  water  flowing 
in  large  amounts  over  the  surface.  Under  such  condi- 
tions the  preparation  of  a  seed  bed,  and  cultivation  of 
the  soil  so  as  to  prevent  washing  are  often  difficult  prob- 
lems. To  prevent  gullying,  the  water  currents  should 
be  divided  as  much  as  possible  by  plowing  narrower 
lands  and  by  increasing  the  number  of  shallow  dead 
furrows.  The  larger  drains  should  be  constructed  with 
the  view  of  preventing  the  formation  of  deep  gullies,  and 
this  can  in  part  be  accomplished  by  encouraging  the 
growth  of  special  grasses  with  fibrous  roots  which  serve 
as  soil  binders.  Soils  which  gully  are  improved  by  the 
addition  of  farm  manures  and  other  humus-forming 
material  which  bind  together  the  soil  particles  ;  also  by 
seeding  and  cultivating  at  right  angles  to  the  slope  of 


PREPARATION    OF    SOILS    FOR    CROPS  3OI 

the  land  so  as  to  break  the  force  of  the  water.  The 
water  should  be  encouraged  to  percolate  through  the 
soil  rather  than  to  flow  over  the  surface.  (See  Section 
25-) 

356.  Bacterial  Diseases  of  Soils.  —  Many  of  the  bac- 
terial diseases  to  which  crops  are  subject  are  caused 
primarily  by  a  diseased  condition  of  the  soil.  These 
diseases  can  often  be  checked  by  the  right  kind  of  culti- 
vation, by  securing  good  drainage,  and  by  proper  soil 
ventilation  supplemented  with  the  application  of  alkaline 
matter  as  wood  ashes  and  land  plaster.  Undrained  soils 
are  unsanitary;  the  products  of  decay  of  the  organic 
matter  accumulate  in  the  soil  and  produce  toxic  or  poi- 
sonous compounds  which  affect  crops.  When  soils  are 
drained,  air  is  admitted  which  prevents  the  formation 
of  these  products.  Both  bacterial  and  fungous  diseases 
of  soils  may  be  controlled  by  cultivation,  particularly 
when  it  improves  the  general  sanitary  condition  of  the 
soil.  With  improvement  in  sanitary  condition,  there 
is  less  liability  of  bacterial  diseases  becoming  established 
and  causing  destruction  of  the  crop.  As  a  result  of 
some  forms  of  bacterial  action,  chemical  substances  in- 
jurious to  plants  are  produced,  and  by  controlling  bac- 
terial action  the  formation  of  these  is  prevented.  Some 
of  the  organisms  propagated  in  the  soil  cause  bacterial 
diseases  of  4airy  and  other  farm  products.  The  use  of 
soil  disinfectants  is  possible  only  where  a  small  area  is 
involved ;  they  are  not  applicable  to  large  tracts  as  they 


3O2  SOILS   AND    FERTILIZERS 

destroy  the  beneficial  as  well  as  the  injurious  soil 
organisms.  A  good  sanitary  condition  of  the  soil  is 
as  essential  for  the  production  of  crops  as  are  suitable 
hygienic  surroundings  for  the  rearing  of  live  stock. 
Sunlight  and  air  are  important  factors  in  bringing  about 
an  improved  sanitary  condition  of  diseased  soils. 

By  the  rotation  of  crops  many  bacterial  diseases,  as 
flax  wilt  and  clover  sickness,  are  controlled.  Some  of 
these  are  disseminated  by  the  use  of  infected  seed. 
By  sprinkling  the  seed  grain  with  a  disinfectant  as  a 
dilute  solution  of  formalin  (i  pound  of  formalin  in  50 
gallons  of  water)  bacterial  diseases,  as  grain  smuts, 
are  held  in  check.  Low  forms  of  plants,  as  fungi, 
also  develop  in  soils  when  conditions  are  favorable, 
and  take  an  important  part  in  changing  the  char- 
acter of  the  soil.  Their  action  may  be  either  beneficial 
or  injurious,  depending  upon  the  condition  of  the  soil. 
There  is  a  very  close  relationship  between  soil  san- 
itation, which  results  in  the  avoidance  of  crop  diseases, 
and  the  quality  and  yield  of  agricultural  products. 

357.  Influence  of  Crowding  Plants  in  the  Seed  Bed.  — 
The  number  of  plants  which  a  seed  bed  should  produce 
is  dependent  mainly  upon  the  supply  of  water  and  plant 
food.  By  means  of  thick  or  thin  seeding,  the  general 
character  of  crops  may  be  influenced  within  definite 
limits.  Either  an  excessive  or  a  scant  amount  of  seed 
gives  poor  results.  If  overcrowded,  plants  fail  to  de- 
velop normally  either  for  want  of  plant  food  or  water,  or 


PREPARATION   OF   SOILS    FOR    CROPS  303 

because  of  poor  sanitary  conditions,  or  from  lack  of 
room  for  development.  Experiments  show  that  an  ex- 
cessive amount  of  seed  wheat  as  more  than  100  pounds 
per  acre  of  spring  wheat  does  not  give  good  results. 
Each  crop  has  its  limit  beyond  which  it  is  not  desirable 
to  crowd  the  plants  in  the  seed  bed.  When  there  is 
crowding,  unhygienic  conditions  prevail  and  the  lack  of 
air,  sunlight,  and  good  ventilation  encourages  bacterial 
diseases,  while  on  the  other  hand  too  few  plants  favor 
the  growth  of  weeds  and  an  abnormal  development  of 
the  crop.  In  the  seeding  of  grains  and  other  farm  crops, 
the  amount  of  seed  to  be  used  per  acre  should  be  deter- 
mined by  the  quality  of  the  seed  and  the  local  conditions, 
as  climate  and  soil,  together  with  any  special  character- 
istic desired  in  the  way  of  composition  and  character  of 
the  crop. 

358.  Selection  of  Crops.  —  The  selection  of  the  most 
suitable  crops  to  be  grown  is  largely  a  local  problem  and 
must  be  determined  by  climatic  and  soil  conditions.  The 
preference  of  farm  crops  for  certain  types  of  soil  is  dis- 
cussed in  Sections  1 1  to  17,  and  it  is  not  advisable  to 
attempt  to  grow  crops  upon  soils  to  which  they  are  not 
naturally  adapted  or  under  unfavorable  climatic  condi- 
tions. Practical  experience  is  the  best  guide  in  re- 
gard to  the  selection  of  crops  and  the  most  suitable 
lines  of  farming  to  follow,  and  it  will  be  found  that  this 
experience  is  in  harmony  with  the  laws  governing  the 
conservation  and  development  of  the  fertility  of  the  soil. 


304  SOILS   AND    FERTILIZERS 

Temporary  methods  of  farming,  as  exclusive  grain  raising, 
can  be  followed  for  a  short  time  on  new  soils  ;  but  it  is 
desirable  that  each  type  of  soil  should  be  subjected  to  a 
judicious  system  of  cultivation,  fertilizing,  and  cropping 
rather  than  to  the  production  of  one  or  only  a  few  mar- 
ket crops  at  random.  The  selection  of  the  crops  and 
their  utilization  for  market  or  feeding  purposes  should 
be  determined  mainly  by  the  system  of  farming  that  is 
most  adapted  to  the  soil  of  the  farm,  and  the  farm 
should  be  managed  largely  with  the  view  of  maintain- 
ing the  fertility  of  the  soil. 

359.  The  Inherent  and  Cumulative  Fertility  of  Soils.95 
—  There  is  present  in  nearly  every  soil  a  variable 
amount  of  inherent  fertility  resulting  from  disintegration 
and  other  changes  to  which  soils  are  subject.  In  some 
long-cultivated  soils  the  amount  of  fertility  produced 
annually  by  weathering  and  natural  agencies  is  sufficient 
to  yield  from  ten  to  fifteen  bushels  of  wheat  per  acre. 
This  does  not  represent  the  maximum  crop-producing 
power  of  the  soil,  but  simply  the  inherent  or  natural  fer- 
tility. When  the  natural  fertility  is  reenforced  with  farm 
manures  and  other  fertilizers,  culmulative  fertility  is 
added  and  maximum  yields  are  secured.  In  many  soils 
there  are  large  amounts  of  cumulative  fertility  or  resi- 
dues from  former  applications  of  manure.  The  crop- 
producing  power  of  a  soil  is  dependent  upon  both  the 
inherent  and  the  cumulative  fertility,  as  well  as  upon 
the  mechanical  condition  of  the  soil.  In  the  production 


PREPARATION   OF   SOILS   FOR    CROPS  305 

of  crops,  all  of  the  inherent  fertility  should  be  utilized  to 
the  best  advantage,  and  cumulative  fertility  should  be 
added  so  that  the  stock  of  total  fertility  may  be  increased. 
Soils  of  the  highest  fertility  are  those  which  are  com- 
posed of  a  large  amount  of  silt  or  particles  of  equivalent 
value,  well  drained,  but  sufficiently  retentive  of  mois- 
ture for  crop  production,  and  of  good  capillarity.  Such 
soils  are  usually  deposited  by  water ;  they  are  uniform 
in  texture,  of  great  depth,  and  contain  large  amounts  of 
organic  matter  rich  in  nitrogen  and  minerals  contain- 
ing all  of  the  essential  elements  of  plant  food.  When 
these  soils  are  cultivated,  the  organic  matter  readily 
undergoes  decay  with  liberation  of  plant  food. 

360.  Balanced  Soil  Conditions.  —  A  high  state  of 
fertility  necessitates  a  balanced  condition  of  the  phys- 
ical and  chemical  properties  of  a  soil.  Some  soils  are 
of  good  texture  and  have  all  the  necessary  physical 
requisites  for  crop  production,  but  fail  to  produce  good 
crops  because  of  a  scant  supply  of  the  essential  elements 
of  plant  food.  Other  soils  contain  the  necessary  plant 
food  but  are  unproductive  because  of  poor  physical 
condition.  Soils  may  be  unproductive  on  account  of 
either  chemical  or  physical  defects,  causing  the  various 
factors  of  soil  fertility  to  be  unbalanced.  In  the  cul- 
tivation of  a  soil  it  should  be  the  aim  to  discover  any 
defect  and  then  to  apply  the  necessary  corrective 
measures.  Soil  problems  are  extremely  varied  in  char- 
acter, and  the  cultivator  of  the  soil  should  seek  aid  jointly 
x 


3O6  SOILS   AND    FERTILIZERS 

from  chemistry,  physics,  biology,  and  geology,  and  also 
from  practical  experience  founded  upon  observation  in 
the  cultivation  of  soils  and  the  production  of  crops. 
The  utilization  and  maintenance  of  the  fertility  of  the 
soil  of  necessity  form  the  basis  of  any  rational  agricul- 
tural system. 


CHAPTER  XIV 
LABORATORY  PRACTICE 

THE  laboratory  practice  is  an  essential  part  of  the  work  in  Soils 
and  Fertilizers,  as  the  experiments  illustrate  many  of  the  funda- 
mental principles  of  the  subject.  The  student  should  endeavor  to 
cultivate  his  powers  of  observation  so  as  to  grasp  the  principles  in- 
volved in  the  work  rather  than  to  do  it  in  a  merely  mechanical  or 
perfunctory  way.  Neatness  is  one  of  the  essentials  for  success  in 
laboratory  practice ;  an  experiment  performed  in  a  slovenly  manner 
is  of  but  little  value. 

A  careful  and  systematic  record  of  the  laboratory  work  should  be 
kept  by  the  student  in  a  suitable  note-book.  In  recording  the  re- 
sults of  an  experiment,  the  student  should  give  in  a  dear  and  con- 
cise form  the  following : 

(1)  Title  of  the  experiment. 

(2)  How  the  experiment  is  performed. 

(3)  What  was  observed. 

(4)  What  the  experiment  proves. 

The  note-book  should  be  a  complete  record  of  the  student's  in- 
dividual work,  and  should  be  written  up  at  the  time  the  experiment 
is  performed. 

Before  an  experiment  is  made  the  student  is  advised  to  review 
those  topics  presented  in  the  text  which  have  a  bearing  upon  the 
experiment,  so  a  clearer  conception  may  be  gained  of  the  relation- 
ship between  the  laboratory  work  and  that  of  the  class  room. 

Students  who  have  had  but  little  laboratory  practice  are  advised 
to  study  the  chapters  on  Laboratory  Manipulation,  and  Water  and 
Dry  Matter,  in  "  The  Chemistry  of  Plant  and  Animal  Life." 

3°7 


308 


SOILS   AND   FERTILIZERS 


Some  of  the  pieces  of  apparatus  are  loaned  to  the  student  when 
needed  to  perform  the  experiment ;  for  these  a  receipt  is  taken,  and 
he  is  credited  with  the  apparatus  when  it  is  returned. 

The  following  are  supplied  to  each  student :  — 


r  Crucible  Tongs. 

I  Pkg.  Filter  Paper. 

i  Test  Tube  Clamp. 

i  Evaporator. 

i  Stirring  Rod. 

3  Beakers. 

6  Test  Tubes. 

i  Test  Tube  Stand. 

i  Funnel. 

i  Mortar  and  Pestle. 


No. 


2  Bottles.  No.  ii 

Large  Cylinder.  12 

Sand  Bath.  13 

Hessian  Crucible.  14 

Wooden  Stand.  15 

Tripod.  1 6 

Ring  Stand  and  3  Rings.  17 

Single  Clamp.  18 
Burner  and  2  Ft.  Rubber 

Tubing.  19 

i  Brush.  20 


Directions  for  Weighing.  —  Place  the  dish  or  material  to  be 
weighed  in  the  left  hand  pan  of  the  balance.  (See  Fig.  51.)  With 
the  forceps  lay  a  weight  from  the  weight  box  on  the  right  hand  pan. 
Do  not  touch  the  weights  with  the  hands.  If  the  weight  selected  is 
too  heavy,  replace  it  with  a  lighter  weight.  Add  weights  until  the 
pans  are  counterpoised ;  this  will  be  indicated  by  the  needle  swing- 
ing nearly  as  many  divisions  on  one  side  of  the  scale  as  on  the  other. 
The  brass  weights  are  the  gram  weights.  The  other  weights  are 
fractions  of  a  gram.  The  500,  200,  100  mg.  (milligram)  weights  are 
recorded  as  .5,  .2,  and  .1  gm.  The  50,  20,  and  10  mg.  weights 
as  0.05,  0.02,  and  o.oi  gm.  If  the  10,  and  2  gm.  and  the  200,  the 
100,  and  the  50  gm.  weights  are  used,  the  resulting  weight  is 
12.35  gms'  No  moist  substance  should  ever  come  in  contact  with 
the  scale  pans.  The  weights  and  forceps  should  always  be  replaced 
in  the  weight  box.  Too  much  care  and  neatness  cannot  be  exer- 
cised in  weighing. 

General  Direction  for  Laboratory  Practice.  —  The  student  should 
write  up  the  results  of  his  experiments  at  the  time  they  are  per- 


LABORATORY   PRACTICE 


309 


formed.  Careful  attention  should  be  given  to  the  spelling,  language, 
and  punctuation,  and  the  note-book  should  represent  the  student's  in- 
dividual work.  He  who  attempts  to  cheat  in  laboratory  work  by 
copying  the  results  of  others  only  cheats  himself.  Care  should  be 
exercised  to  prevent  anything  getting  into  the  sinks  that  will  clog 


FlG.  51.    Balance  and  Weights. 

the  plumbing ;  soil,  matches,  broken  glass,  and  paper  should  be  de- 
posited in  the  waste  jars.  The  student  should  learn  to  use  his 
time  in  the  laboratory  profitably  and  economically.  He  should  ob- 
tain a  clear  idea  of  what  he  is  to  do,  and  then  do  it  to  the  best  of 
his  ability.  If  the  experiment  is  not  a  success,  repeat  it.  While 
the  work  is  in  progress  it  should  be  given  undivided  attention. 


SOILS   AND    FERTILIZERS 

Experiment  No.  i 

Determination  of  the  Hydroscopic  Moisture  and  Volatile  Matter  of 

Soils 


FIG.  52.  Apparatus  for  determining  Moisture  Content  of  Soils. 

Weigh  in  grams  to   the  second   decimal  place  a   dry  Hessian 
crucible.      Place   5   to    10  gms.  of  air-dried   soil    in  the  crucible 


LABORATORY   PRACTICE 


and  weigh  again.  Then  place  the  dish  containing  the  soil  in  the 
water  oven  and  leave  it  four  hours  for  the  soil  to  dry.  Cool  and 
weigh  at  once  so  there  may  be  as 
little  absorption  of  water  from  the 
air  as  possible.  From  the  loss  of 
weight,  calculate  the  per  cent  of 
hydroscopic  moisture  in  the  soil. 
Place  the  crucible  containing  the 
dry  soil  in  a  muffle  furnace  and 
leave  until  all  of  the  organic  mat- 
ter is  volatilized.  After  the  cru- 
cible has  cooled  on  an  asbestos 
mat,  weigh  and  calculate  the  per 
cent  of  volatile  matter.  The  vola- 
tile matter  consists  of  organic  mat- 
ter and  water  that  is  held  in  chemi- 
cal combination  with  the  silicates. 
(Soils  from  the  students'  home 
farms  are  to  be  used  in  Experi- 
ments Nos.  i,  2,  4,  6,  9,  12,  16, 18, 
19,  and  21,  each  student  working 
with  his  own  soil.)  pro.  S3.  Muffle  Furnace  used  for  de- 

termining Volatile  Matter. 

Experiment  No.  2 

Determination  of  the  Capacity  of  Loose  Soils  to  absorb  Water 
To  100  gms.  of  air-dried  soil  in  a  beaker  add  100  cc.  of  water. 
Mix  the  soil  and  water,  then  pour  the  mixture  on  a  saturated 
but  not  dripping  filter  paper  fitted  into  a  funnel.  For  transfer- 
ring the  soil,  50  cc.  more  water  may  be  used.  Measure  the  drain 
water  in  a  graduate.  To  prevent  evaporation,  keep  the  moist  soil 
in  the  funnel  covered  with  a  glass  plate.  Deduct  the  leachings 
from  the  total  water  used.  Calculate  the  per  cent  of  water  retained 
by  the  air-dried  soil. 


312 


SOILS   AND    FERTILIZERS 


Repeat  the  experiment,  using  sand,  and  note  the  difference  in 
absorptive  power. 

Repeat,  using  95  per  cent  of  sand  and  5  per  cent  of  dry  and 
finely  pulverized  manure. 

Experiment  No.  3 

Determination  of  the  Capillary  Water  of  Soils 
For  this  experiment  a  sample  of  soil  directly  from  the  field  is 

to  be  used.  The  sample  is  to  be 
taken  at  a  depth  of  from  3  to  9 
inches  or  at  any  depth  desired. 
One  hundred  grams  of  soil  are 
weighed  into  a  tared  drying  pan, 
exposed  in  a  thin  layer  to  the  room 
temperature  for  24  hours  and  then 
reweighed.  After  an  interval  of 
from  two  to  four  hours  the  soil  is 
weighed  again,  and  if  the  weight  is 
fairly  constant,  the  per  cent  of  water 
lost  by  air  drying,  representing  the 
capillary  water  of  the  soil  at  the  time 
of  sampling,  is  calculated.  This  ex- 
periment may  be  repeated,  using 
different  types  of  soil,  as  sand,  clay, 
and  loam. 

Experiment  No.  4 

Capillary  Action  of  Water  upon 
Soils 

FIG.  54.    The  Capillary  Water  of         Firmly  tie  a  piece  of  linen  cloth 
Soils.  over  the  end  of  a  long  glass  tube 

4  inches   in   diameter,   then  fasten   a  piece   of  wire  gauze    over 
the  cloth.     Fill  the  tube  with  sandy  soil  (No.  i).    Compact  the  soil 


LABORATORY   PRACTICE  $13 

after  the  addition  of  each  measured  quantity  by  allowing  the  weight 
from  the  compaction  machine  (see  Experiment  No.  8)  to  drop  twice 
from  the  12 -inch  mark. 

In  a  similar  way,  fill  a  second  and  a  third  tube  with  clay 
and  loam  respectively  ;  immerse  the  lower  ends  of  the  tubes  in 
a  cylinder  of  water  and  support  the  tubes,  as  shown  in  the  illus- 
tration. Measure  each  day  for  one  week  the  height  to  which  the 
water  rises  in  the  soils.  If  desired,  three  more  tubes  filled  loosely 
with  the  soils  may  be  added,  and  the  influence  of  compaction 
upon  the  capillary  rise  of  water  in  the  soils  noted. 

Experiment  No.  5 

Influence  of  Manure  and  Shallow  Surface  Cultivation  upon  the 
Moisture  Content  and  Temperature  of  Soils 

Weigh  and  fill  four  boxes,  each  a  foot  square  and  a  foot  deep, 
as  follows  :  one  with  air-dried  sand,  one  with  day,  one  with  loam,  and 
one  with  sand  containing  5  per  cent  of  fine  dry  manure.  Deter- 
mine the  hydroscopic  moisture  of  each  sample.  Weigh  the  boxes 
after  adding  the  soils  which  should  be  moderately  compacted.  To 
each  add  the  same  amount  of  water  slowly  from  a  sprinkling  pot, 
carefully  measuring  the  water  used.  The  soil  should  be  well  mois- 
tened, but  not  supersaturated.  Each  box  is  to  receive  shallow  sur- 
face cultivation,  using  for  the  purpose  a  gardener's  small  tool.  Leave 
the  boxes  exposed  to  the  sun  or  in  a  moderately  warm  room.  At  the 
end  of  one  or  two  days  take  a  sample  of  soil  from  the  center  of 
each  box  at  a  depth  of  4  to  8  inches  and  determine  the  moisture 
content  as  directed  in  Experiment  No.  i.  Note  the  differences  in 
moisture  content.  Weigh  the  boxes.  Take  the  temperature  of  the 
soil  in  each  box. 

Experiment  No.  6 
Weight  of  Soils 

Determine  the  cubic  contents  of  a  box  about  4  inches  square. 
Weigh  the  box.  Determine  its  weight  when  filled,  not  compacted, 


SOILS    AND    FERTILIZERS 


with  air-dry  sand,  with  clay,  with  loam,  and  with  peaty  soil.     Com- 
pute the  weight  per  cubic  foot  of  each  soil.     Calculate  the  weight 

.        , of  water  held   by  the 

box.  Determine  the  ap- 
parent specific  gravity. 

Experiment  No.  7 
Influence  of  Color  upon 
the   Temperature  of 
Soils 

Expose  to  the  sun's 
rays,  dry  clay,  dry  sand, 
and  moist  and  dry  peat. 
After  two  hours'  expo- 
sure take  the  tempera- 
ture of  each.     The  bulb 
of    the     thermometer 
ight  per  Cubic  Foot    should  be  just  covered 
with  the  soil.     All  of 
the  observations  should  be  made  under  uniform  conditions. 


FlG.  55.    Determining  the  We 
of  Soils. 


Experiment  No.  8 
Movement  of  Air  through  Soils 

Fill,  without  compacting,  a  soil  tube  12  inches  high  and  3  inches 
in  diameter  with  sifted  loam  soil.  Nearly  fill  the  outer  cylinder  with 
water,  open  the  stopcock,  and  allow  the  inner  cylinder  to  sink  in 
the  water,  close  the  stopcock  and  connect  the  aspirator  to  the  soil  tube 
with  a  rubber  tube.  Adjust  the  weight,  2,  open  the  stopcock,  and 
note  the  time  required  for  5  liters  of  air  to  aspirate  through  the  soil. 
In  like  manner  fill  tubes  with  sand,  gravel,  peat,  and  clay,  and  deter- 
mine the  time  required  for  5  liters  of  air  to  be  aspirated  through 
each.  In  filling  the  tubes,  care  should  be  taken  that  all  are  treated 
alike.  Repeat  the  experiment,  using  soil  from  your  own  farm  loosely 


LABORATORY   PRACTICE  31$ 

filling  one  tube,  and  moderately  compacting  another  with  the  com- 
pacting machine.  Note  the  difference  in  time  required  for  the  air 
to  pass  through  the  loose  and  the  compacted  soil. 


FIG.  56.    Aspirator  for  determining  the  Rate  of  Movement  of  Air  through  Soils. 
(Adapted  from  Bui.  107,  U.  S.  Dept.  Agr.,  Office  of  Expt.  Stations.) 

Experiment  No.  9 
Separation  of  Sand,  Silt,  and  Clay 

For  this  experiment  the  student  should  use  some  of  the  soil  from 
his  home  farm.     Ten  grams  of  air-dried  and  crushed  soil  which  have 


SOILS   AND    FERTILIZERS 

been  passed  through  a  sieve  with  holes  0.5  mm.  in  diameter  are 
placed  in  a  mortar  and  about  20  cc.  of  water  added.  The  soil  is 
pestled  with  a  rubber-tipped  pestle  with  the  object  of  separating 
adhering  particles  without  pulverizing  the  individual  soil  grains. 
After  two  or  three  minutes'  pestling,  more  water  is  added  and  the 
soil  and  water  are  allowed  to  sediment  for  about  one  minute ;  the 
turbid  liquid  is  then  decanted  into  a  beaker.  This  process  of  soft 

pestling  and  decan- 
tation  is  repeated 
two  or  three  times 
until  the  remaining 
soil  grains  appear 
free  from  adhering 
smaller  particles. 
With  some  soils 
this  is  a  tedious 
process.  The  con- 
tents of  the  mortar 
are  the?  transferred 
to  the  beaker  and 

enough  water  added 
FIG.  57.    The  Mechanical  Analysis  of  Soils.  tQ     nearjy    fjU     tne 

beaker.  The  contents  of  the  beaker  are  thoroughly  stirred,  and  after 
two  or  three  minutes'  sedimentation,  the  turbid  liquid  is  decanted 
into  a  second  beaker,  leaving  the  sediment  in  the  first  beaker.  More 
water  is  added  to  the  first  beaker,  and  the  stirring,  sedimentation, 
and  decantation  are  repeated  until  the  sediment  consists  mainly  of 
clean  fine  sand.  After  about  ten  minutes  the  turbid  liquid  in  the 
second  beaker  is  decanted  into  a  large  cylinder,  the  sediment  in  the 
beaker  being  washed  with  more  water  and  the  washings  added  to  the 
cylinder.  It  is  to  be  noted  that  the  sediment  in  the  second  beaker 
is  composed  of  finer  particles  than  the  sediment  in  the  first  beaker. 
The  sediment  in  the  first  beaker  consists  mainly  of  medium  and  fine 
sand,  and  in  the  second  beaker  of  fine  sand  and  coarse  silt.  Some 


LABORATORY   PRACTICE 


317 


sand  particles  are  carried  along  in  the  washings  into  the  large  cylinder. 
It  is  difficult  to  make  even  an  approximate  separation  of  a  soil  into 
sand,  silt,  and  clay  particles.  In  the  mechanical  analysis  of  soil,  the 
chemist  uses  the  microscope 
to  determine  when  the  sepa- 
rations are  reasonably  com- 
plete. The  sediment  in  the 
cylinder  consists  mainly  of 
silt.  The  fine  particles  which 
remain  suspended  in  the  water 
of  the  cylinder  and  cause  the 
roiled  appearance  are  mainly 
the  clay  particles.  In  this 
experiment  note  approxi- 
mately what  grades  of  soil 
particles  predominate  in  your 
soil.  Save  the  liquid  in  the 
cylinder  for  the  next  experi- 
ment. 

Experiment  No.  10 
Sedimentation  of  Clay 

In  each  of  three  separate 
cylinders  or  beakers  place 
200  cc.  of  ^he  turbid  liquid 
saved  from  Experiment  No. 
9.  To  beaker  No.  I,  add  0.5 
gm.  calcium  hydroxide  and  FIG.  58.  Movement  of  Water  through  Soils, 
stir.  To  beaker  No.  2,  add 

i  gm.  of  calcium  hydroxide  and  stir.  The  third  beaker  is  used  for 
purposes  of  comparison  and  no  calcium  hydroxide  is  added.  After 
24  hours  examine  the  three  beakers  and  note  the  influence  of  the 
calcium  hydroxide  in  precipitating  the  clay  and  clarifying  the  liquid. 


318  SOILS   AND   FERTILIZERS 

Experiment  No.  n 
Deportment  of  Soils  when  Wet 

Place  about  5  gms.  of  the  soil  used  in  Experiment  No.  9  in  the 
palm  of  the  hand.  Wet  and  knead.  Note  whether  a  plastic  mass 
is  formed.  If  the  soil  is  sticky,  it  indicates  the  presence  of  plastic 
clay.  Rub  some  of  the  soil  between  thumb  and  finger ;  if  it  is  com- 
posed largely  of  clay,  it  will  feel  smooth  and  oily.  The  sand  parti- 
cles impart  a  sharp  gritty  feeling ;  in  the  presence  of  clay  this  is  more 
or  less  modified.  Note  whether  the  lumps  of  dry  soil  crush  easily. 
The  way  a  soil  responds  when  crushed,  wet,  and  kneaded,  gives 
some  idea  of  its  tillage  properties. 

Experiment  No.  12 
Rate  of  Movement  of  Water  through  Soils 

Weigh  a  soil  tube  and  fill  it  to  within  two  inches  of  the  top  with 
sand.  Weigh  again.  In  like  manner  weigh  and  fill  two  other 
tubes,  one  with  clay  and  one  with  loam.  Support  the  tubes  from 
the  ring  stand  as  noted  in  Fig.  No.  58.  Place  a  receptacle  under 
the  outlet  of  each  tube.  Measure  into  cylinders  or  large  beakers 
three  500  cc.  portions  of  water.  From  one  of  these  beakers  slowly 
pour  the  water  into  the  sand  cylinder,  and  note  the  length  of  time 
required  for  the  water  to  percolate  through  the  sand,  and  the  amount 
of  water  that  percolates  in  a  given  time.  Replenish  the  water  in 
the  beaker  with  measured  amounts  as  needed.  In  like  manner  test 
the  clay  and  the  loam.  After  the  water  has  ceased  dripping  from 
the  tubes,  weigh  and  calculate  the  amount  retained  by  the  soils. 

Experiment  No.  13 
Properties  of  Rocks  from  which  Many  Soils  are  Derived 

Study  the  laboratory  samples  of  rocks  and  fill  out  the  following 
table:  — 


LABORATORY    PRACTICE 


319 


ROCKS 

COMPARATIVE 
HARDNESS 

COLOR 

GENERAL 
FORM 

SOLUBLE 
IN  HC1 

Feldspar  .... 
Mica 





Quartz  .... 
Granite  .... 
Hornblende  .  .  . 
Limestone  .  .  . 





Experiment  No.  14 
Form  and  Size  of  Soil  Particles 

(Note.  Special  directions  for  manipulating  the  microscope,  plac- 
ing the  material  on  the  microscopical  object  slide,  and  focusing  will 
be  given  by  the  instructor.) 

Place  on  a  microscopical  object  slide  a  small  amount  of  soil ;  dis- 
tribute it  in  a  thin  layer,  and  examine  with  a  low-power  microscope. 
Observe  the  form  and  size  of  the  soil  particles,  distinguish  the  vari- 
ous grades  of  sand,  silt,  and  clay,  and  make  drawings  of  some  of  the 
particles. 

Experiment  No.  15 

Pulverized  Rock  Particles 

Examine  with  a  low-power  microscope  samples  of  pulverized 
mica,  feldspar,  granite,  and  limestone.  Note  any  similarity  to  the 
soil  particles  examined  in  Experiment  No.  14. 

Experiment  No.  16 
Reaction  of  Soils 

For  this  experiment  use  peaty,  mildly  alkaline,  and  clay  soils. 
Bring  in  contact  with  each  soil,  after  moistening  with  distilled 
water,  pieces  of  sensitive  red  and  blue  litmus  paper.  Note  any 
changes  in  color  of  the  litmus  paper  and  state  what  the  results  show. 
In  a  similar  way  test  the  soil  from  your  own  farm. 


32O  SOILS   AND   FERTILIZERS 

Experiment  No.  17 
Absorption  of  Gases  by  Soils 

Weigh  50  gms.  of  soil  into  a  wide-mouthed  bottle,  add  50  cc.  of 
water  and  i  cc.  of  strong  ammonia.  Note  the  odor.  Cork  the 
bottle,  shake,  and  after  24  hours  again  note  the  odor.  To  what  is 
the  fixation  of  the  ammonia  due?  Is  this  a  physical  or  a  chemical 
change?  Define  fixation. 

Experiment  No.  18 
Acid  Insoluble  Matter  of  Soils 

Weigh  10  gms.  of  soil  into  a  beaker,  add  100  cc.  hydrochloric 
acid  (50  cc.  strong  acid  and  50  cc.  H2O)  ;  cover  the  beaker  with  a 
watch  glass ;  heat  on  the  sand  bath  in  the  hood  for  two  hours,  re- 
placing the  acid  solution  in  case  excessive  evaporation  takes  place. 
Filter,  transfer,  and  wash  the  residue,  using  50  cc.  distilled  water. 
Note  the  appearance  and  quantity  of  insoluble  residue.  Of  what 
does  it  co.nsist?  What  is  its  value  as  plant  food?  How  does  it 
resemble  the  original  soil  and  in  what  ways  does  it  differ?  Save 
the  filtrate  for  the  next  experiment. 

Experiment  No.  19 
Acid  Soluble  Matter  of  Soils 

Divide  the  filtrate  from  the  preceding  experiment  into  three 
equal  portions,  (i)  To  one  portion  add  ammonia  until  alkaline. 
The  precipitate  formed  consists  of  iron  and  aluminum  hydroxide  and 
phosphoric  acid.  Note  the  color  and  gelatinous  appearance  of  this 
precipitate.  When  dried  it  occupies  only  a  small  volume.  Filter 
and  remove  this  precipitate  which  contains  lime,  magnesia,  potash, 
and  soda.  To  the  filtrate  add  20  cc.  of  ammonium  oxalate ;  warm 
on  the  sand  bath,  and  note  any  precipitate  of  calcium  oxalate 
that  is  formed.  (2)  Evaporate  the  second  portion  nearly  to  dry- 
ness.  Add  20  cc.  distilled  H2O  and  3  cc.  HNO3 ;  warm  to  dissolve 


LABORATORY   PRACTICE  321 

any  residue.  Add  5  to  7  cc.  of  ammonium  molybdate,  heat  gently, 
and  shake.  The  yellow  precipitate  is  ammonium  phosphomolyb- 
date,  which  contains  the  element  P  in  mechanical  and  chemical  com- 
bination. (3)  Evaporate  the  third  portion  in  the  evaporating  dish 
on  the  sand  bath.  Of  what  does  the  residue  consist  and  what 
elements  does  it  contain? 

Experiment  No.  20 
Extraction  of  Humus  from  Soils 

Place  10  gms.  of  soil  in  a  bottle  (preferably  a  glass-stop- 
pered one)  and  add  200  cc.  H2O  and  5  cc.  HC1.  Shake  and  allow 
10  to  24  hours  for  the  acid  to  dissolve  the  lime  so  the  humus 
can  be  dissolved  by  the  alkali.  Filter  the  acid  and  wash  the  soil 
on  the  filter  with  distilled  water  until  the  washings  are  no  longer 
acid  to  litmus  paper.  Transfer  the  soil  to  the  bottle  again,  add 
100  cc.  H2O  and  5  cc.  KOH  solution.  Shake,  and  after  two  to 
four  hours  filter  off  some  of  the  solution  which  is  dark-colored 
and  contains  dissolved  humus  compounds. 

To  10  cc.  of  the  filtered  humus  solution  add  HC1  until  neutral. 
The  precipitate  formed  is  mainly  humic  acid  and  soil  humates. 
Evaporate  a  second  portion  of  10  to  20  cc.  to  dryness ;  the  black 
residue  obtained  is  humus  material  extracted  from  the  soil. 

Experiment  No.  21 

Nitrogen  in  Soils 

Mix  5  gms.  of  soil  and  an  equal  bulk  of  soda  lime  in  a  mortar; 
transfer  to  a  strong  test  tube.  Connect  the  test  tube  with  a  deliv- 
ery tube  which  leads  into  another  test  tube  containing  distilled 
water.  Heat  cautiously  for  from  5  to  10  minutes,  with  the  Bunsen 
burner,  the  test  tube  containing  the  soil  and  soda  lime.  Test  the 
liquid  with  litmus  paper  and  note  the  reaction.  Soda  lime  aided 
by  heat  decomposes  the  organic  matter  of  the  soil  and  forms  CO2, 
H2O,  and  NH3.  The  nitrogen  in  the  form  of  ammonia  is  distilled 
Y 


322 


SOILS   AND    FERTILIZERS 


and  absorbed  by  the  water  in  the  second  test  tube;  the  reaction 
is  due  to  the  presence  of  the  ammonia. 


Experiment  No.  22 
Testing  for  Nitrates 

Dissolve  about  50  milligrams  of  sodium  or  potassium  nitrate  in 

loo  cc.  H2O.  To  15  cc. 
of  this  solution  add  2  cc. 
of  a  dilute  and  clear  solu- 
tion of  FeSO4,  and  place 
the  test  tube  in  a  cylinder. 
Through  a  long-stemmed 
funnel  add  2  or  3  cc.  H2SO4. 
Observe  the  dark  brown 
ring  that  is  formed ;  H2SO4 
liberates  HNO3  as  a  free 
acid,  which  in  turn  changes 
the  iron  from  the  ferrous 
to  the  ferric  state ;  the  dark 
brown  color  is  due  to  the 
nitric  acid  forming  interme- 
diate compounds  during 
FIG.  59.  Testing  for  Nitrates.  this  operation. 


Experiment  No.  23 
Volatilization  of  Ammonium  Salts 

In  separate  test  tubes  place  about  o.i  gm.  each  of  ammonium 
carbonate  and  ammonium  sulphate.  Apply  heat  gently  to  each  and 
observe  the  result.  Observe  that  the  ammonium  carbonate  readily 
volatilizes  and  some  is  deposited  on  the  walls  of  the  test  tube  while 
the  ammonium  sulphate  is  much  less  volatile.  In  poorly  ventilated 
barns,  deposits  of  ammonium  carbonate  are  frequently  found. 


LABORATORY    PRACTICE 


323 


Experiment  No.  24 
Testing  for  Phosphoric  Acid 

Dissolve  0.5  gm.  bone  ash  in  15  cc.  H2O  and  3  to  5  cc.  HNO3  and 
filter.  To  the  warm  filtrate  add  5  to  7  cc.  ammonium  molybdate 
and  shake.  The  yellow  precipitate  formed  is  ammonium  phospho- 
molybdate.  See  Experiment  No.  19. 

In  a  test  tube  heat  0.5  gm.  of  bone  ash  with  20  cc.  distilled 
H2O ;  filter.  To  the  warm  filtrate  add  5  cc.  ammonium  molyb- 
date and  shake.  Note  the  result  as  compared  with  that  when 
HNO3  was  used  with  the  distilled  water.  What  does  the  result 
show  ? 

Experiment  No.  25 
Preparation  of  Acid  Phosphate 

Place  100  gms.  bone  ash  in  a  large  lead  dish.  Add  slowly  and 
with  constant  stirring  100  gms.  commercial 
sulphuric  acid,  using  an  iron  spatula  for  the 
purpose.  Transfer  the  mixture  to  a  wooden 
box  and  allow  it  to  act  for  about  three  days. 
Then  pulverize  and  examine.  The  mixing  of 
the  acid  and  phosphate  should  be  done  in  a 
place  where  there  is  a  good  draft.  Test  % 
gm.  for  water  soluble  phosphates  as  directed 
in  Experiment  No.  24. 

Experiment  No.  26 

Solubility  of  Organic  Nitrogenous  Compounds 
in  Pepsin  Solution 

Prepare  a  pepsin  solution  by  dissolving 
5  gms.  of  commercial   pepsin  in  a  liter  of 

water,  adding  i  cc.  of  strong  HC1.     Place  in    , 

FIG.  60.     Determining 

separate  beakers  0.5  gm.  each  of  dried  blood,  Digestibility  of  Organic 
tankage,  and  bone  ash.  Add  200  cc.  of  pep-  Nitrogen  in  Acid  Pepsin 
gin  solution  to  each  and  place  the  beakers  in  a  Solution. 


324  SOILS   AND    FERTILIZERS 

water  bath  kept  at  a  temperature  of  about  40°  C.  Stir  occasion- 
ally, and  at  the  end  of  five  hours  observe  and  compare  the  amounts 
of  insoluble  matter  remaining  in  the  beakers,  note  also  the  color 
and  appearance  of  the  solution  in  each  beaker.  See  Section  170. 

Experiment  No.  27 

Preparation  of  Fertilizers 

Mix  in  a  box  200  gms.  acid  phosphate  (saved  from  Experiment 
No.  25),  50  gms.  kainit,  and  50  gms.  sodium  nitrate.  Calculate  the 
percentage  composition  of  this  fertilizer  and  its  trade  value. 

Experiment  No.  28 

Testing  Ashes 

Test  samples  of  leached  and  unleached  ashes  in  the  way  de- 
scribed in  Section  256. 

Experiment  No.  29 
Extracting  Water  Soluble  Materials  from  a  Commercial  Fertilizer 

Dry  and  weigh  a  7  cm.  filter  paper.  Fit  it  in  a  funnel,  and  place 
in  it  2  gms.  of  commercial  fertilizer.  Pass  through  the  filter,  a  little 
at  a  time,  a  half  liter  of  pure  water  at  about  40°  C.  (distilled 
water  preferred) .  Transfer  the  filter  paper  and  contents  to  a  watch 
glass,  dry  in  a  water  oven,  weigh  and  calculate  the  per  cent  of 
material  extracted  by  the  water.  If  the  fertilizer  is  made  of  such 
materials  as  acid  phosphate,  kainit,  muriate  or  sulphate  of  potash, 
nitrate  of  soda  and  sulphate  of  ammonia,  from  60  to  90  per  cent 
will  dissolve.  Inspect  the  insoluble  residue  and  note  if  it  is 
composed  of  dried  blood,  bones,  or  animal  refuse  material.  Of  a 
high-grade  complete  commercial  fertilizer  from  40  to  80  per  cent 
or  more  should  dissolve  in  water. 


LABORATORY   PRACTICE  32$ 

Experiment  No.  30 

Influence  of  Continuous  Cultivation  and  Crop  Rotation   upon  the 
Properties  of  Soils 

For  this  experiment  a  soil  that  has  been  under  continuous  culti- 
vation, and  also  one  of  similar  character  from  an  adjoining  field 
where  the  crops  have  been  rotated  and  farm  manures  have  been 
applied,  should  be  used.  Make  the  following  determinations  with 
each  soil :  — 

Weight  per  cubic  foot. 

Capacity  to  hold  water. 

Note  the  color  of  each. 

Experiment  No.  31 
Summary  of  Results  of  Tests  with  Home  Soil 

Make  a  tabulation  of  your  results  including : 

Hydroscopic  moisture  as  determined  in  Experiment  No.  I. 

Volatile  matter  as  determined  in  Experiment  No.  I. 

Capacity  of  the  loose  soil  to  absorb  water,  Experiment  No.  2. 

Height  of  rise  of  capillary  water  in  tube,  Experiment  No.  4. 

Weight  per  cubic  foot,  Experiment  No.  6. 

Prevailing  kind  of  soil  particles,  Experiment  No.  9. 

Deportment  of  soil  when  wet  and  kneaded,  Experiment  No.  1 1. 

Reaction  of  soil,  Experiment  No.  16. 

Amount  of  acid  soluble  matter,  Experiment  No.  19. 

Amount  of  lime,  Experiment  No.  19. 

Amount  of  humus  extractive  material,  Experiment  No.  20. 

Crops  most  suitable  for  production  upon  this  soil  as  indicated  by 
physical  and  chemical  tests. 

How  does  this  agree  with  your  experience  with  the  crops  raised 
on  the  soil? 

Probable  deficiencies  or  weak  points  as  indicated  by  tests  or  past 
experience. 

What  is  the  most  suitable  line  of  farming  to  follow  with  this  soil 
in  order  to  conserve  its  fertility? 


326  SOILS  AND    FERTILIZERS 

Scheme  of  Soil  Classification 

(Adapted  from  Bureau  of  Soils  Report,  U.  S.  Dept.  Agr.) 

Coarse  sand  contains  more  than  20  per  cent  of  coarse  sand  and 
more  than  50  per  cent  of  fine  gravel,  coarse  sand,  and  medium  sand, 
less  than  10  per  cent  of  very  fine  sand,  less  than  15  per  cent  of  silt, 
less  than  10  per  cent  of  clay,  and  less  than  20  per  cent  of  silt  and 
clay. 

Medium  sand  contains  less  than  10  per  cent  of  fine  gravel,  more 
than  50  per  cent  of  coarse,  medium,  and  fine  sand,  less  than  10  per 
cent  of  very  fine  sand,  less  than  15  per  cent  of  silt,  less  than  10  per 
cent  of  clay,  and  less  than  20  per  cent  of  silt  and  clay. 

Fine  sand  contains  less  than  10  per  cent  of  fine  gravel  and 
coarse  sand,  more  than  50  per  cent  of  fine  and  very  fine  sand,  less 
than  15  per  cent  of  silt,  less  than  10  per  cent  of  clay,  and  less  than 
20  per  cent  of  silt  and  clay. 

Sandy  loam  contains  more  than  20  per  cent  of  fine  gravel,  coarse 
sand  and  medium  sand,  more  than  20  per  cent  and  less  than  35 
per  cent  of  silt,  less  than  15  per  cent  of  clay,  and  less  than  50  per 
cent  of  silt  and  clay. 

Fine  sandy  loam  contains  more  than  40  per  cent  of  fine  and 
very  fine  sand  and  more  than  20  per  cent  and  less  than  50  per  cent 
of  silt  and  clay,  usually  10  to  35  per  cent  of  silt  and  from  5  to  15 
per  cent  of  clay. 

Silt  loam  contains  more  than  55  per  cent  of  silt  and  less  than  25 
per  cent  of  clay. 

Loam  contains  less  than  55  per  cent  of  silt  and  more  than  50 
per  cent  of  silt  and  clay,  usually  from  15  to  25  per  cent  of  clay. 

Clay  loam  contains  from  25  to  55  per  cent  of  silt,  25  to  35  per 
cent  of  clay,  and  more  than  60  per  cent  of  silt  and  clay. 

Clay  contains  more  than  35  per  cent  of  clay. 

Sandy  clay  contains  more  than  30  per  cent  of  coarse,  medium, 
and  fine  sand,  less  than  25  per  cent  of  silt,  more  than  20  per  cent  of 
clay,  and  less  than  60  per  cent  of  silt  and  clay. 

Silt  clay  contains  more  than  55  per  cent  of  silt  and  from  25  to  35 
per  cent  of  clay. 


REVIEW  QUESTIONS 

CHAPTER  I 

I.  From  what  are  soils  derived  ?  2.  What  are  the  physical  prop- 
erties of  soils  ?  When  do  soils  differ  physically,  when  chemically  ? 
3.  Why  do  soils  differ  in  weight?  Arrange  clay,  sand,  loam,  and 
peat  in  order  of  weight  per  cubic  foot.  4.  When  wet,  what  would 
be  the  order?  5.  What  is  the  absolute  and  what  the  apparent 
specific  gravity  of  soils  ?  What  is  pore  space  ?  6.  Define  the  terms : 
skeleton,  fine  earth,  fine  sand,  silt,  and  clay.  7.  What  are  the 
physical  properties  of  clay  ?  8.  What  are  the  forms  of  the  soil 
particles  ?  9.  How  do  different  types  of  soil  vary  as  to  the  number 
of  particles  per  gram  of  soil  ?  10.  How  is  a  mechanical  analysis 
of  a  soil  made  ?  1 1 .  Why  do  certain  crops  thrive  best  on  definite 
types  of  soil  ?  12.  What  factors  must  be  taken  into  consideration 
in  determining  the  type  to  which  a  soil  belongs  ?  13.  Give  the 
mechanical  structure  of  a  good  potato  soil.  14.  How  does  a  wheat 
soil  differ  in  mechanical  structure  from  a  truck  soil?  15.  A  good 
corn  soil  is  also  a  type  for  what  other  crops  ?  16.  How  much 
water  is  required  to  produce  an  average  grain  crop,  and  how  do  the 
rainfall  and  the  water  removed  in  crops  during  the  growing  season 
compare  ?  17.  In  what  forms  may  water  be  present  in  soils  ?  18. 
What  is  bottom  water  and  when  may  it  be  utilized  by  crops  ?  19. 
What  is  capillary  water  ?  20.  Explain  the  capillary  movement  of 
water.  21.  Explain  how  the  capillary  and  non-capillary  spaces  in 
the  soil  may  be  influenced  by  cultivation.  22.  What  is  hydroscopic 
water  and  of  what  value  is  it  to  crops  ?  23.  What  is  percolation  ? 
24.  To  what  extent  may  losses  occur  by  percolation  ?  25.  What 
are  the  factors  which  influence  evaporation  ?  26.  What  is  transpira- 
tion ?  27.  In  what  three  ways  may  water  be  lost  from  the  soil  ? 
28.  Why  does  shallow  surface  cultivation  prevent  evaporation  ? 

327 


328  SOILS    AND    FERTILIZERS 

29.  Why  is  it  necessary  to  cultivate  the  soil  after  a  rain  ?  30.  Ex- 
plain the  movement  of  the  soil  water  after  a  light  shower.  31 .  What 
influence  has  rolling  the  land  upon  the  moisture  content  of  the  soil? 
32.  What  is  subsoiling  and  how  does  it  influence  the  moisture 
content  of  soils  ?  33.  What  influence  does  early  spring  plowing 
exert  upon  the  soil  moisture  ?  34.  What  is  the  action  of  a  mulch 
upon  the  soil  ?  35.  Why  should  different  soils  be  plowed  to  differ- 
ent depths  ?  36.  What  is  meant  by  the  permeability  of  a  soil? 
37.  How  may  cultivation  influence  permeability?  38.  How  may 
commercial  fertilizers  influence  the  water  content  of  soils  ?  39. 
Explain  the  physical  action  of  well-prepared  farm  manures  upon  the 
soil  and  their  influence  upon  the  soil  water.  40.  What  is  the  object 
of  good  drainage  ?  41.  Why  does  deforesting  a  region  unfavorably 
influence  the  agricultural  value  of  a  country  ?  42.  What  are  the 
sources  of  heat  in  soils  ?  43.  To  what  extent  does  the  color  of 
soils  influence  the  temperature  ?  44.  What  is  the  specific  heat  of 
soils?  45.  To  what  extent  does  drainage  influence  soil  tempera- 
ture and  how  does  cultivation  affect  soil  temperature  ?  46.  How 
do  manured  and  unmanured  lands  compare  as  to  temperature  ?  47. 
What  relation  does  heat  bear  to  crop  growth  ?  48.  What  materials 
impart  color  to  soils  ?  49.  What  is  the  effect  of  loss  of  organic 
matter  upon  the  color  of  soils  ?  50.  What  materials  impart  taste  to 
soils  ?  Odor  ?  51.  What  effect  does  a  weak  current  of  electricity 
have  upon  crop  growth  ?  52.  Do  all  soils  possess  the  same  power 
to  absorb  gases  ?  Why  ? 

CHAPTER  n 

53.  What  is  agricultural  geology  ?  54.  What  agencies  have 
taken  part  in  soil  formation?  55.  How  does  the  action  of  heat, 
cold,  air,  and  gases  aid  in  soil  formation  ?  56.  Explain  the  physical 
action  of  water  in  soil  formation.  Explain  its  chemical  action.  57. 
What  is  glacial  action,  and  how  has  it  been  an  important  factor  in 
soil  formation  ?  58.  Explain  the  action  of  earthworms  and  vegeta- 
tion upon  soils.  59.  How  have  micro-organisms  aided  in  soil  forma- 


REVIEW    QUESTIONS  329 

tion  ?  60.  Explain  the  terms :  sedentary,  transported,  alluvial, 
colluvial,  volcanic,  and  wind-formed  soils.  61.  What  is  feldspar 
and  what  kind  of  soil  does  it  produce  ?  62.  Give  the  general 
composition  of  the  following  rocks  and  minerals  and  state  the 
kind  of  soil  which  each  produces :  granite,  mica,  hornblende, 
zeolites,  kaolin,  apatite,  and  limestone. 

CHAPTER  HI 

63.  What  elements  are  liable  to  be  the  most  deficient  in  soils  ? 
64.  Name  the  acid-  and  base-forming  elements  present  in  soils.  65. 
What  are  the  elements  most  essential  for  crop  growth  ?  66.  State 
some  of  the  different  ways  in  which  the  elements  present  in  soils 
combine.  67.  Why  is  it  customary  to  speak  of  the  oxides  of  the 
elements  and  to  deal  with  them  rather  than  with  the  elements  ?  68. 
Do  the  elements  exist  in  the  soil  in  the  form  of  oxides  ?  69.  What 
are  double  silicates  ?  70.  In  what  forms  does  carbon  occur  in  soils  ? 
71.  Is  the  soil  carbon  the  source  of  the  plant  carbon  ?  72.  What 
can  you  say  regarding  the  occurrence  and  importance  of  the  sulphur 
compounds  ?  73.  What  influence  would  o.io  per  cent  chlorine  have 
upon  the  soil  ?  74.  In  what  forms  does  phosphorus  occur  in 
soils  ?  75.  What  is  the  principal  form  in  which  nitrogen  occurs 
in  soils  ?  76.  What  can  be  said  regarding  the  hydrogen  and 
oxygen  of  the  soil  ?  77.  State  the  principal  forms  and  the  value  as 
plant  food  of  the  following  elements :  aluminum,  potassium,  calcium, 
sodium,  and  iron.  78.  For  plant-food  purposes,  what  three 
divisions  are  made  of  the  soil  compounds  ?  79.  Why  are  the 
complex  silicates  of  no  value  as  plant  food  ?  80.  Give  the  relative 
amounts  of  plant  food  in  the  three  classes.  81.  How  is  a  soil 
analysis  made  ?  82.  What  can  be  said  regarding  the  economic 
value  of  a  soil  analysis  ?  83.  What  are  some  of  the  important  facts 
to  observe  in  interpreting  results  of  soil  analysis  ?  84.  Under  what 
conditions  are  the  results  most  valuable  ?  85.  Do  the  terms  '  volatile 
matter 'and 'organic  matter' mean  the  same  ?  86.  How  may  organic 
acids  be  employed  in  soil  analysis  ?  87.  Why  are  dilute  organic 


33O  SOILS   AND   FERTILIZERS 

acids  used  ?  88.  Is  the  plant  food  equally  distributed  in  both  sur- 
face and  subsoil  ?  89.  Do  different  grades  of  soil  particles,  from 
the  same  soil,  have  the  same  composition  ?  90.  What  are  '  alkali 
soils'?  91.  Why  is  the  alkali  sometimes  in  the  form  of  a  crust? 
What  is  black  alkali  ?  92.  Are  all  soils  with  white  coating  strongly 
alkaline?  93.  Give  the  treatment  for  improving  an  alkali  soil.  94. 
How  may  a  small  'alkali  spot'  be  treated?  95.  What  are  the 
sources  of  the  organic  compounds  of  soils  ?  What  are  acid  soils  ? 
96.  How  may  the  organic  compounds  of  the  soil  be  classified  ?  97. 
Explain  the  term 'humus.'  98.  How  is  the  humus  of  the  soil  ob- 
tained ?  99.  What  is  humification  ?  What  is  a  humate  ?  How 
are  humates  produced  in  the  soil  ?  100.  Explain  how  different 
materials  produce  humates  of  different  value.  101.  Arrange  in 
order  of  agricultural  value  the  humates  produced  from  the  following 
materials  :  oat  straw,  sawdust,  meat  scraps,  sugar,  clover.  102.  Of 
what  value  are  the  humates  as  plant  food  ?  103.  How  much  plant 
food  is  present  in  soils  in  humate  forms  ?  104.  What  agencies  cause 
a  decrease  of  the  humus  content  of  soils  ?  105.  To  what  extent 
does  humus  influence  the  physical  properties  of  soils  ?  106.  What 
is  humic  acid  ?  107.  What  soils  are  most  liable  to  be  in  need 
of  humus  ?  When  are  soils  not  in  need  of  humus  ?  108.  In  what 
ways  does  the  humus  of  long-cultivated  soils  differ  from  that  of  new 
soils  ?  109.  How  may  different  methods  of  farming  influence  the 
humus  content  of  soils  ? 

CHAPTER  IV 

no.  What  may  be  said  regarding  the  importance  of  nitrogen  as 
plant  food  ?  in.  What  are  the  functions  of  nitrogen  in  plant  nu- 
trition ?  112.  How  may  the  foliage  indicate  a  lack  or  an  excess  of 
this  element  ?  113.  In  what  three  ways  did  Boussingault  conduct 
experiments  relating  to  the  assimilation  of  the  free  nitrogen  of  the 
air?  114.  What  were  his  results?  115.  What  conclusions  did 
Ville  reach  ?  116.  Give  the  results  of  Lawes  and  Gilbert's  experi- 
ments. 117.  How  did  field  results  compare  with  laboratory  experi- 


REVIEW    QUESTIONS  331 

ments  ?  118.  In  what  ways  were  the  conditions  of  field  experi- 
ments different  from  those  conducted  in  the  laboratory  ?  119.  Give 
the  results  of  Hellriegel's  and  Wilfarth's  experiments.  120.  What 
is  noticeable  regarding  the  composition  of  clover-root  nodules  ?  121 . 
Of  what  agricultural  value  are  the  results  of  Hellriegel  ?  122.  What 
is  the  source  of  the  soil's  nitrogen  ?  123.  How  may  the  organic 
nitrogen  compounds  of  the  soil  vary  as  to  complexity  ?  124.  To 
what  extent  may  the  nitrogen  in  soils  vary  ?  125.  To  what  extent 
is  nitrogen  removed  in  crops?  126.  To  what  extent  are  nitrates, 
nitrites,  and  ammonium  compounds  found  in  soils  ?  127.  To  what 
extent  is  nitrogen  returned  to  the  soil  in  rain  water  ?  128.  How 
may  the  ratio  of  nitrogen  to  carbon  vary  in  soils  ?  Of  what  agricul- 
tural value  is  this  ratio  ?  129.  Under  what  conditions  do  soils  gain 
in  nitrogen  content  ?  130.  What  methods  of  cultivation  cause  the 
most  rapid  decline  in  the  nitrogen  content  of  soils,  and  how  can  a 
nitrogen  equilibrium  be  maintained  in  the  soil  ?  131.  What  is 
nitrification  ?  132.  What  are  the  conditions  necessary  for  nitrifica- 
tion, and  what  are  the  food  requirements  of  the  nitrifying  organ- 
ism ?  133.  Why  is  oxygen  necessary  for  nitrification  ?  134.  How 
do  temperature,  moisture,  and  sunlight  influence  this  process  ? 
135.  What  part  do  calcium  carbonate  and  other  basic  compounds 
take  in  nitrification  ?  136.  How  is  nitrous  acid  produced  ?  137. 
What  is  denitrification  ?  138.  What  other  organisms  are  present  in 
soils  besides  those  which  produce  nitrates,  nitrites,  and  ammonia  ? 

139.  What  chemical  products  do  these  various  organisms  produce  ? 

140.  Why  are  soils  sometimes  inoculated  with  organisms?     When 
is   this  necessary  and  when  is  it  not  ?     141.   Why  does  summer 
fallowing  of  rich  land  cause  a  loss  of  humus  and  nitrogen?     142. 
What  influence  have  deep  and  shallow  plowing,  and  spring  and  fall 
plowing,  upon  the  available  soil  nitrogen  ?     143.    Into  what  three 
classes  are  nitrogenous  fertilizers  divided  ?     144.   How  is  dried  blood 
obtained  ?    What  is  its  composition,  and  how  is  it  used  ?     145. 
What  is  tankage  ?     How  is  it  used,  and  how  does  it  differ  in  com- 
position from  dried  blood  ?     146.   What  is  flesh  meal  ?     147.   What 


332  SOILS   AND   FERTILIZERS 

is  fish-scrap  fertilizer,  and  what  is  its  comparative  value  ?  148. 
What  seed  residues  are  used  as  fertilizer  ?  What  is  their  value  ? 
149.  What  methods  are  employed  to  detect  the  presence  of  leather, 
hair,  and  wool  waste  in  fertilizers  ?  Why  are  these  materials  objec- 
tionable ?  150.  How  may  peat  and  muck  be  used  as  fertilizers? 
151.  What  is  sodium  nitrate  ?  How  is  it  used,  and  what  is  its  value 
as  a  fertilizer?  152.  How  does  ammonium  sulphate  compare  in 
fertilizer  value  with  nitrate  of  soda  ?  What  is  calcium  cyanamid  ? 
153.  What  is  the  difference  between  the  nitrogen  content  and  the 
ammonia  content  of  fertilizers  ? 

CHAPTERS  V  AND  VI 

154.  What  is  fixation  ?  What  is  absorption  ?  Give  an  illus- 
tration. 155.  To  what  is  fixation  due  ?  156.  What  part  does 
humus  take  in  fixation  ?  157.  Why  do  soils  differ  in  fixative 
power  ?  Why  are  nitrates  not  fixed  ?  Explain  the  fixation  of 
potash,  phosphate,  and  ammonium  compounds.  158.  Why  is  fixa- 
tion a  desirable  property  of  soils  ?  159.  Why  is  it  necessary  to 
study  the  subject  of  fixation  in  the  use  of  manures  ?  Why  is  the 
soil  solution  dependent  upon  the  fixative  power  of  the  soil  ?  160. 
Why  are  farm  manures  variable  in  composition  ?  161.  What  is 
the  distinction  between  the  terms  'stable  manure'  and  'farmyard 
manure'  ?  162.  About  what  per  cent  of  nitrogen,  phosphoric  acid, 
and  potash  is  present  in  ordinary  manure  ?  163.  Coarse  fodders 
cause  an  increase  of  what  element  in  the  manure  ?  164.  What 
four  factors  influence  the  composition  and  value  of  manure  ?  165. 
What  influence  do  absorbents  .have  upon  the  composition  of 
manures  ?  166.  What  advantages  result  from  the  use  of  peat  and 
muck  as  absorbents  ?  167.  Compare  the  value  of  manure  produced 
from  clover  with  that  from  timothy  hay.  168.  How  may  the  value 
of  manure  be  determined  from  the  nature  of  the  food  consumed  ? 
169.  To  what  extent  is  the  fertility  of  the  food  returned  in 
the  manure  ?  170.  Is  much  nitrogen  added  to  the  body  during  the 
process  of  fattening  ?  171.  Explain  the  course  of  the  nitrogen  of 


REVIEW    QUESTIONS  333 

the  food  during  digestion  and  the  forms  in  which  it  is  voided  in 
the  manure.  172.  Compare  the  solid  and  liquid  excrements  as  to 
constancy  of  composition  and  amounts  produced.  173.  What  is 
meant  by  the  manurial  value  of  food  ?  174.  Name  five  foods  with 
high  manurial  value  ;  also  five  with  low  manurial  value.  175. 
What  is  the  usual  commercial  value  of  manures  compared  with 
commercial  fertilizers  ?  176.  How  does  the  manure  from  young 
and  from  old  animals  compare  as  to  value  ?  177.  How  much 
manure  does  a  well-fed  cow  produce  per  day  ?  178.  What  are  the 
characteristics  of  cow  manure  ?  How  do  horse  manure  and  cow 
manure  differ  as  to  composition,  character,  and  fermentability  ? 
179.  What  are  the  characteristics  of  sheep  manure  ?  180.  How 
does  hen  manure  differ  from  any  other  manure  ?  181.  Why  should 
the  solid  and  liquid  excrements  be  mixed  to  produce  balanced 
manure  ?  182.  What  volatile  nitrogen  compound  may  be  given  off 
from  manure  ?  183.  What  may  be  said  regarding  the  use  of  human 
excrements  as  manure  ?  184.  Is  there  any  danger  of  immediate 
scarcity  of  plant  food  to  necessitate  the  use  of  human  excrements 
as  manure  ?  185.  To  what  extent  may  losses  occur  when  manures 
are  exposed  in  loose  piles  and  allowed  to  leach  for  six  months  ? 
1 86.  What  two  classes  of  ferments  are  present  in  manure  ?  How 
does  an  application  of  farm  manure  affect  the  bacterial  content  of 
soil  and  what  influence  does  this  have  upon  the  plant  food  of  the 
soil  ?  187.  Explain  the  workings  of  the  two  classes  of  ferments 
found  in  manures.  188.  How  much  heat  may  be  produced  in 
manure  during  fermentation  ?  189.  Is  water  injurious  to  manure  ? 
190.  How  should  manure  be  composted  ?  What  is  gained  ?  191. 
How  does  properly  composted  manure  compare  in  composition  with 
fresh  manure  ?  192.  Explain  the  action  of  calcium  sulphate  in  the 
preservation  of  manure.  193.  How  does  manure  produced  in 
barn  yards  compare  in  composition  and  crop-producing  value  with 
that  produced  in  covered  sheds  ?  194.  When  may  manure  be 
taken  directly  to  the  field  and  spread  ?  195.  How  may  coarse 
manures  be  injurious  to  crops  ?  196.  What  is  gained  by  manuring 


334  SOILS   AND    FERTILIZERS 

pasture  land  ?  197.  Is  it  economical  to  make  a  number  of  small 
manure  piles  in  a  field  ?  Give  reason.  198.  At  what  rate  per 
acre  may  manure  be  used  ?  199.  To  what  crops  is  it  not  advisable 
to  add  stable  manure  ?  200.  How  do  a  crop  and  the  manure  pro- 
duced from  that  crop  compare  in  manurial  value?  201.  Why  do 
manures  have  such  a  lasting  effect  upon  soils  ?  202.  Why  does 
manure  from  different  farms  vary  so  much  in  value  and  composi- 
tion ?  203.  In  what  ways  may  stable  manures  be  beneficial  ? 

CHAPTER  VH 

204.  What  may  be  said  regarding  the  importance  of  phosphorus 
as  plant  food  ?  What  function  does  it  take  in  plant  economy  ? 
205.  What  is  phosphoric  acid  and  how  much  is  removed  in  ordi- 
nary farm  crops  ?  206.  To  what  extent  is  phosphoric  acid  present 
in  soils  ?  207.  What  are  the  sources  of  the  soil's  phosphoric  acid  ? 

208.  What  are  the  commercial  sources  of  phosphate  fertilizers  ? 

209.  Name  the  four  calcium  phosphates  and  give  their  relative  fer- 
tilizer values.     210.   Define  reverted  phosphoric  acid.     211.   Define 
available    phosphoric   acid.     212.    In   what    forms    do   phosphate 
deposits  occur  ?     213.    State  the  general  composition  of  phosphate 
rock.    214.  Explain  the  process  by  which  acid  phosphates  are  made. 
Give  reactions.     215.   How  is  the  commercial  value  of  phosphoric 
acid  determined  ?    216.   What  is  basic  phosphate  slag  and  what  is 
its  value  as  a  fertilizer  ?     217.   What  is  guano  ?     218.   How  do  raw 
bone  and  steamed  bone  compare  as  to  field  value  ?     As  to  composi- 
tion ?    219.   What  is  dissolved  bone  ?     220.   How  is   bone  black 
obtained,  and  what   is   its  value   as  a  fertilizer  ?     221.   How  are 
phosphate  fertilizers  applied   to  soils  ?     In  what  amounts  ?     222. 
How  may  the  phosphoric  acid  of  the  soil  be  kept  in  available 
condition  ? 

CHAPTER  VHI 

223.  What  is  the  function  in  plant  nutrition  of  potassium  ?  224. 
What  is  potash  and  to  what  extent  is  it  removed  in  farm  crops  ? 
225.  To  what  extent  is  potash  present  in  soils  ?  226.  What  are 


REVIEW   QUESTIONS  335 

the  sources  of  the  soil's  potash  ?  227.  What  are  the  various  sources 
of  the  potash  used  for  fertilizers  ?  228.  What  are  the  Stassfurt  salts, 
and  how  are  they  supposed  to  have  been  formed  ?  229.  What  is 
kainit  ?  230.  How  much  potash  is  there  in  hard  wood  ashes  ?  231. 
In  what  ways  do  ashes  act  on  soils  ?  232.  How  do  unleached  ashes 
differ  from  leached  ashes  ?  233.  What  is  meant  by  the  alkalinity 
of  an  ash  ?  234.  Of  what  value,  as  fertilizer,  are  hard-  and  soft- 
coal  ashes  ?  235.  What  is  the  fertilizer  value  of  the  ashes  from 
tobacco  stems  ?  236.  Cottonseed  hulls  ?  237.  Peat-bog  ashes  ? 
238.  Sawmill  ashes  ?  239.  Lime-kiln  ashes  ?  240.  How  is  the 
commercial  value  of  potash  determined  ?  241.  How  are  potash 
fertilizers  used  ?  242.  Why  is  it  sometimes  necessary  to  use  a  lime 
fertilizer  in  connection  with  a  potash  fertilizer  ? 

CHAPTER  IX 

243.  What  can  be  said  regarding  the  importance  of  calcium  as  a 
plant  food  ?  244.  What  is  lime,  and  to  what  extent  is  it  removed 
in  crops  ?  245.  To  what  extent  do  soils  contain  lime  ?  246.  What 
are  the  lime  fertilizers  ?  247.  Explain  the  physical  action  of  lime 
fertilizers.  248.  Explain  the  action  of  lime  on  heavy  clays.  249. 
On  sandy  soils.  250.  In  what  ways,  chemically,  do  lime  fertilizers 
act  ?  251.  How  may  lime  aid  in  liberating  potash  ?  252.  What  is 
marl  ?  253.  How  are  lime  fertilizers  applied  ?  254.  What  is  the 
result  when  land  plaster  is  used  in  excess  ?  255.  Explain  the  action 
of  salt  on  soils.  256.  When  would  it  be  desirable  to  use  salt  as  a 
fertilizer  ?  257.  Is  soot  of  any  value  as  a  fertilizer  ?  Explain  its 
action.  258.  Are  seaweeds  of  any  value  as  fertilizer  ?  What  is  the 
fertilizer  value  of  street  sweepings  ?  Of  garbage  ? 

CHAPTER  X 

259.  What  is  a  commercial  fertilizer?  An  amendment?  260. 
To  what  does  the  commercial  fertilizer  industry  owe  its  origin? 

261.  Why  are  commercial   fertilizers  so  variable  in  composition? 

262.  Explain  how  a  commercial  fertilizer  is  made.     263.   Why  are 


SOILS   AND    FERTILIZERS 

analysis  and  inspection  of  fertilizers  necessary?  264.  What  are 
the  usual  forms  of  nitrogen  in  commercial  fertilizers?  265.  Of 
phosphoric  acid  and  potash  ?  266.  How  is  the  value  of  a  commer- 
cial fertilizer  determined?  267.  What  is  gained  by  home  mixing 
of  fertilizers?  268.  What  can  be  said  about  the  importance  of 
tillage  when  fertilizers  are  used?  269.  How  are  commercial  fer- 
tilizers sometimes  injudiciously  used?  270.  How  may  field  tests 
be  conducted  to  determine  a  deficiency  in  available  nitrogen,  phos- 
phoric acid,  or  potash?  271.  To  determine  a  deficiency  of  two 
elements?  272.  How  are  the  preliminary  results  verified?  273. 
Why  is  it  essential  that  field  tests  with  fertilizers  be  made?  274. 
Under  what  conditions  does  it  pay  to  use  commercial  fertilizers? 
275.  What  is  the  result  when  commercial  fertilizers  are  used  in 
excessive  amounts?  276.  Under  ordinary  conditions,  what  special 
help  do  the  following  crops  require :  wheat,  barley,  corn,  potatoes, 
mangels,  turnips,  clover,  and  timothy?  277.  In  what  ways  do 
commercial  fertilizers  and  farm  manures  differ?  How  do  they  com- 
pare in  crop-producing  value  ? 

CHAPTER  XI 

278.  Does  the  amount  of  fertility  removed  by  crops  indicate  the 
nature  of  the  fertilizer  required?  In  what  ways  are  plant-ash 
analyses  valuable  ?  279.  Explain  the  action  of  plants  in  rendering 
their  own  food  soluble.  To  what  extent  does  the  soil  solution  sup- 
ply plant  food?  280.  Why  do  crops  differ  as  to  their  power  of  pro- 
curing food?  281.  Why  is  wheat  grown  on  a  clay  soil  less  liable 
to  need  potash  than  nitrogen?  282.  What  position  should  wheat 
occupy  in  a  rotation?  283.  In  what  ways  do  wheat  and  barley 
differ  in  feeding  habits  ?  284.  What  can  be  said  regarding  the  food 
requirements  of  oats?  285.  Corn  removes  from  the  soil  twice  as 
much  nitrogen  as  a  wheat  crop,  yet  wheat  usually  thrives  after 
corn.  Why?  What  help  is  corn  most  liable  to  need  in  the  way 
of  food?  286.  What  is  flax  wilt?  287.  What  position  should  flax 
occupy  in  a  rotation?  288.  On  what  soils  does  flax  thrive  best? 


REVIEW    QUESTIONS  337 

289.  What  is  the  essential  point  to  observe  in  the  manuring  of 
potatoes?  290.  What  kind  of  manuring  is  required  by  sugar  beets  ? 
291.  Why  should  the  manuring  of  mangels  be  different  from  that  of 
turnips?  292.  What  may  be  said  regarding  the  food  requirements 
of  buckwheat  and  rape?  293.  What  kind  of  manuring  do  hops  and 
cotton  require?  294.  What  kind  of  manuring  is  most  suitable  for 
leguminous  crops?  For  garden  crops,  for  orchards,  and  lawns? 

CHAPTER  XII 

295.  What  is  the  object  of  rotating  crops?  296.  Should  the 
whole  farm  undergo  the  same  rotation  system?  297.  What  is 
meant  by  soil  exhaustion?  298.  What  are  the  important  princi- 
ples to  be  observed  in  a  rotation?  299.  Explain  why  it  is 
essential  that  deep-  and  shallow-rooted  crops  should  alternate? 
300.  Why  is  it  necessary  that  humus  be  considered  in  a  rota- 
tion? 301.  What  is  the  object  of  growing  crops  of  dissimilar  feed- 
ing habits?  302.  How  may  crop  residues  be  used  to  the  best 
advantage?  303.  How  is  decline  of  soil  nitrogen  prevented  by 
a  good  rotation  of  crops?  304.  In  what  ways  do  different 
crops  and  their  cultivation  influence  the  mechanical  condition 
of  the  soil?  305.  How  may  the  best  use  be  made  of  the  soil 
water?  306.  How  may  a  rotation  make  an  even  distribution  of 
farm  labor?  307.  How  are  manures  used  to  the  best  advantage  in 
a  rotation?  308.  In  what  other  ways  are  rotations  advantageous? 

309.  What  may  be  said  regarding  long-  and  short-course  rotations  ? 

310.  How  is  the  conservation  of  fertility  best  secured  ?    311.   Why 
does  the  use  made  of  crops  influence  fertility?    312.   What  are  the 
essential  points  to  be  observed  in  the  two  systems  of  farming  com- 
pared in  Section  344?    313.   Is  it  essential  that  all  elements  re- 
moved in  crops  be  returned  to  the  soil  in  exactly   the  amounts 
contained  in  the  crops?    Why?    314.   How  does  manure  influence 
the  inert    matter  of    the    soil?    315.    What  general    systems  of 
farming    best    conserve    fertility?    316.     Under    what    conditions 
may  farms  be  gaining  in  reserve  fertility?     317.   Why  in  continued 

z 


338  SOILS    AND    FERTILIZERS 

grain  culture  does  the  loss  of  nitrogen  from  a  soil  exceed  the 
amount  removed  in  the  crop?  Will  a  crop  rotation  alone  maintain 
the  fertility  of  the  soil  ? 

CHAPTER  Xm 

318.  Why  do  soils  need  further  treatment  than  plowing  for  the 
preparation  of  the  seed  bed  ?  319.  Why  should  different  soils  receive 
different  methods  of  treatment  in  the  preparation  of  the  seed  bed  ? 
320.  How  would  you  determine  the  best  treatment  to  give  a  soil  for 
the  preparation  of  the  seed  bed?  321.  How  do  different  methods  of 
plowing  influence  the  condition  of  the  seed  bed?  322.  Why  does 
complete  inversion  of  sod  frequently  form  a  poor  seed  bed?  323. 
How  should  the  plowing  be  done  to  form  a  good  seed  bed?  324. 
Why  is  it  economy  to  pulverize  the  soil  as  much  as  possible  when 
it  is  plowed?  325.  What  effect  does  the  moisture  content  of  the 
soil  at  the  time  of  plowing  have  upon  the  condition  of  the  seed 
bed?  326.  What  effect  does  an  excess  of  moisture  have  upon  the 
plowing  and  working  of  clay  soils  ?  327.  In  what  condition  should 
the  seed  bed  be  left  as  to  fineness?  328.  What  is  gained  by  fining 
and  moderately  firming  the  seed  bed?  329.  Why  is  aeration  of 
the  soil  necessary?  330.  Why  do  different  soils  require  different 
degrees  of  aeration?  331.  Under  what  conditions  can  the  seed 
bed  be  prepared  without  plowing?  332.  On  what  kinds  of  soil  is 
such  a  practice  not  advisable?  333.  When  is  it  advisable  to  mix 
the  subsoil  with  the  surface  soil?  334.  When  is  it  not  desirable 
to  mix  the  surface  soil  and  subsoil?  335.  How  can  the  plowing 
and  cultivation  of  the  soil  best  be  carried  on  to  destroy  weeds? 
336.  In  what  way  does  cultivation  influence  bacterial  action  in  the 
soil?  337.  What  classes  of  compounds  in  the  soil  are  subject  to 
bacterial  action?  338.  How  does  the  action  of  bacteria  affect  the 
supply  of  available  plant  food?  339.  What  is  meant  by  inocu- 
lation of  soils  ?  340.  In  what  two  ways  can  this  be  accomplished? 
341.  What  soils  are  most  improved  by  inoculation?  342.  What 
soils  are  least  in  need  of  inoculation  ?  343.  What  other  treatment 
must  often  be  combined  with  inoculation  ?  344.  Why  do  different 


REVIEW    QUESTIONS  339 

crops  require  different  cultivation?  345.  How  can  the  best  kind  of 
cultivation  for  a  crop  be  determined?  346.  How  can  soils  best  be 
cultivated  to  prevent  washing  and  gullying?  347.  What  treatment 
should  such  soils  receive  to  be  permanently  improved?  348.  What 
relationship  exists  between  bacterial  diseases  of  soils  and  of  crops? 
349.  What  treatment  should  soils  receive  to  prevent  bacterial 
diseases?  350.  How  can  the  spreading  of  bacterial  diseases 
through  infected  seed  be  prevented?  351.  Why  must  the  sanitary 
condition  of  a  soil  be  considered  ?  352.  Whatare  the  effects  of  some 
forms  of  fungi  upon  soils?  353.  In  what  way  does  thick  or  thin 
seeding  affect  plant  growth?  354.  What  effect  does  abnormal 
crowding  of  plants  have  upon  growth  ?  355.  How  would  you  deter- 
mine the  amount  of  seed  for  crop  production?  356.  How  would 
you  determine  the  most  suitable  crop  for  any  soil?  357.  What  should 
be  the  aim  in  selecting  crops  for  soils?  358.  Why  should  the  crop 
selected  vary  with  different  types  of  soil?  359.  What  is  the  in- 
herent fertility  of  soils?  360.  What  is  the  cumulative  fertility  of 
soils?  361.  How  can  the  total  fertility  of  soils  be  best  increased? 
362.  Describe  soils  of  the  highest  fertility.  363.  Why  must  the 
amount  of  plant  food  as  well  as  the  physical  condition  of  the  soil  be 
considered  in  the  improvement  of  soils?  364.  What  relation  does 
the  fertility  of  the  soil  bear  to  any  agricultural  system  ? 


1 .  VENABLE  :   History  of  Chemistry. 

2.  GILBERT  :  Inaugural  Lecture,  University  of  Oxford. 

3.  LIEBIG  :    Chemistry  in   Its   Applications   to   Agriculture  and 

Physiology. 

4.  GILBERT  :  The  Scientific  Principles  of  Agriculture  (Lecture). 

5.  SNYDER:   Minnesota  Agricultural  Experiment  Station  Bulletin 

No.  30. 

6.  WILEY  :  Agricultural  Analysis,  Vol.  I. 

7.  HILGARD  :  Soils. 

8.  Maryland  Agricultural  Experiment  Station  Bulletin  No.  21. 

9.  SNYDER  :   Minnesota  Agricultural  Experiment  Station  Bulletin 

No.  41. 

10.  OSBORNE  :  Journal  of  Analytical  Chemistry,  Vol.  II,  Part  3. 

11.  Bureau  of  Soils.     Numerous  bulletins  on  soil  types. 

12.  HELLRIEGEL  :  Calculated  from  Beitrage  zu  den  Naturwissen- 

schaft  Grandlagen  des  Ackerbaus. 

13.  KING  :    Wisconsin   Agricultural  Experiment  Station   Report, 


14.  Unpublished  results  of  author. 

15.  KING  :  Soils. 

1 6.  ROBERTS  :  Fertility  of  the  Land. 

17.  STOCKBRIDGE  :  Rocks  and  Soils. 

18.  SNYDER:   Minnesota  Agricultural  Experiment  Station  Bulletin 

No.  53. 

19.  WHITNEY  :  Division  of  Soils,  U.  S.  Department  of  Agriculture 

Bulletin  No.  6. 

20.  MERRILL  :  Rocks,  Rock-weathering,  and  Soils. 

34° 


REFERENCES  341 

21.  MUNTZ  :    Comptes  Rendus   de   1'Academie  des  Sciences,  CX 

(1890). 

22.  STOKER  :  Agriculture,  Vol.  I. 

23.  DYER  :  Journal  of  the  Chemical  Society,  March,  1894. 

24.  Goss  :  Association  of  Official   Agricultural  Chemists   Report, 

1896;  also  SNYDER  :   Minnesota  Experiment  Station  Bulletin 
No.  102. 

25.  PETER  :  Association  of  Official  Agricultural  Chemists  Report, 

1895  ;  also  Journal  Analytical  and  Applied  Chemistry,  Vol. 
VII,  No.  6. 

26.  LOUGHRIDGE  :  American  Journal  of  Science,  Vol.  VII  (1874). 

27.  HILGARD  :  Year-book  U.  S.  Department  of  Agriculture,  1895. 

28.  HOUSTON:   Indiana  Agricultural   Experiment  Station  Bulletin 

No.  46. 

29.  MULDER  :  From  Mayer  ;  Lehrbuch  der  Agrikulturchemie,  2. 

30.  WHEELER  :    Rhode  Island  Agricultural   Experiment   Station 

Reports,  1892,  1893,  etc. 

31.  Year-book  U.  S.  Department  Agriculture,  1895. 

32.  LOUGHRIDGE  :  South  Carolina  Agricultural  Experiment  Station 

Second  Annual  Report. 

33.  Association  of  Official  Agricultural  Chemists  Report,  1893. 

34  Washington  Agricultural  Experiment  Station  Bulletin  No.  13. 

35.  Association  of  Official  Agricultural  Chemists  Report,  1894. 

36.  California  Agricultural  Experiment  Station  Report,  1890. 

37.  SNYDER  :   Minnesota  Agricultural  Experiment  Station  Bulletin 

No.  29. 

38.  SNYDER  :   Minnesota  Agricultural  Experiment  Station  Bulletin 

No.  47. 

39.  LAWES  AND  GILBERT  :  Experiments  on  Vegetation,  Vol.  I. 

40.  BOUSSINGAULT  :  Agronomic,  Tome  I. 

41.  ATWATER  :   American  Chemical  Journal,  Vol.  VI,  No.  8,  and 

Vol.  VIII,  No.  5. 

42.  HELLRIEGEL  :  Welche  Stickstoffe  Quellen  stehen  der  Pflanze 

zu  Gebote  ? 


342  SOILS   AND    FERTILIZERS 

43.  SNYDER  :    Minnesota  Agricultural  Experiment  Station  Bulletin 

No.  34. 

44.  WARINGTON  :  U.  S.  Department  of  Agriculture,  Office  of  Ex- 

periment Stations  Bulletin  No.  8. 

45.  HILGARD  :    Association  of  Official  Agricultural  Chemists  Re- 

port, 1895. 

46.  MARCHAL  :  Journal  of  the  Chemical  Society  (abstract),  June, 

1894. 

47.  KifNNEMANN  :  Die  Landwirthschaftlichen  Versuchs-Stationen, 

50  (1898). 

48.  ADAMETZ  :  Abstract,  Biedermann's  Centralblatt  fur  Agrikultur- 

chemie,  1887. 

49.  ATWATER  :  American  Chemical  Journal,  Vol.  IX  (1887). 

50.  STUTZER  :  Biedermann's  Centralblatt  fur  Agrikulturchemie,  1883. 

51.  JENKINS  :   Connecticut  State  Agricultural  Experiment  Station 

Report,  1893. 

52.  Bulletin  107,  U.  S.  Department  of  Agriculture,  Bureau  of  Chem- 

istry, Official  Methods. 

53.  Journal  of  the  Royal  Agricultural  Society,  1850. 

54.  From  SACHSSE  :  Lehrbuch  der  Agrikulturchemie. 

55.  LA  WES  AND  GILBERT  :  Experiments  with  Animals. 

56.  BEAL  :  U.  S.   Department  of  Agriculture,   Farmers'   Bulletin 

No.  21. 

57.  SNYDER  :   Minnesota  Agricultural  Experiment  Station  Bulletin 

No.  26. 

58.  Mainly  from  ARMSBY  :  Pennsylvania  Agricultural  Experiment 

Station  Report,  1890.     Figures   for  grains  calculated   from 
original  data. 

59.  HEIDEN  :  Dungelehre. 

60.  LIEBIG  :  Natural  Laws  of  Husbandry. 

61.  Cornell  University  Agricultural  Experiment   Station  Bulletins 

Nos.  13,  27,  and  56. 

62.  KINNARD  :  From  Manures  and  Manuring  by  Aikman. 

63.  WYATT  :  Phosphates  of  America. 


REFERENCES  343 

64.  WILEY  :  Agricultural  Analysis,  Vol.  III. 

65.  GOESSMANN  :   Massachusetts  Agricultural  Experiment   Station 

Report,  1894. 

66.  Connecticut  (State)  Agricultural  Experiment  Station  Bulletin 

No.  103. 

67.  GOESSMANN  :   Massachusetts  Agricultural  Experiment  Station 

Report,  1896. 

68.  LIPMAN  AND   VOORHEES  :   U.  S.  Department   of  Agriculture, 

Office  of  Experiment  Stations  Bulletin  194. 

69.  BOUSSINGAULT  :  From  STOKER  :  Agriculture. 

70.  Handbook  of  Experiment  Station  Work. 

71.  New  York  (State)  Agricultural   Experiment  Station   Bulletin 

No.  1 08. 

72.  VOORHEES  :  U.  S.  Department  of  Agriculture,  Fanners'  Bulle- 

tin No.  44. 

73.  LIEBIG  :  Die  Chemie  in  ihrer  Anwendung  auf  Agrikultur  und 

Physiologic. 

74.  WARINGTON  :  Chemistry  of  the  Farm. 

75.  LA  WES  AND  GILBERT  :  Growth  of  Wheat. 

76.  LA  WES  AND  GILBERT  :  Growth  of  Barley. 

77.  LUGGER  :    Minnesota  Agricultural  Experiment  Station  Bulle- 

tin No.  13. 

78.  LA  WES  AND  GILBERT  :  Growth  of  Potatoes. 

79.  SNYDER  :   Minnesota  Agricultural  Experiment  Station  Bulletin 

No.  56. 

80.  SHAW  :   U.  S.  Department  of  Agriculture,  Farmers'   Bulletin 

No.  11. 

81.  WHITE  :  U.  S.  Department  of  Agriculture,  Farmers'  Bulletin 

No.  48. 

82.  LA  WES  AND  GILBERT  :  Permanent  Meadows. 

83.  THOMPSON,  PORTEUS  :  Graduating  Essay,  Minnesota  School  of 

Agriculture. 

84.  NEFEDOR  :    Abstract,    Experiment    Station    Record,    Vol.   X, 

No.  4. 


344  SOILS   AND    FERTILIZERS 

85.  SNYDER  :  Minnesota  Agricultural  Experiment  Station  Bulletin 

No.  89. 

86.  CONN  :  Agricultural  Bacteriology. 

87.  New  York    Agricultural    Experiment   Station   Bulletins   Nos. 

270,  282. 

88.  MEYER  :  Outlines  of  Theoretical  Chemistry. 

89.  VOORHEES  :  Fertilizers. 

90.  Cornell  University  Experiment  Station  Bulletin  No.  103. 

91.  FRAPS  :  Annual  Report  1904,  Association  Official  Agricultural 

Chemists. 

92.  Illinois  Experiment  Station  Bulletin  No.  93. 

93.  Canadian  Experiment  Farms  Report,  1903,  etc. 

94.  D.  Land.  Vers.  Stat.,  1899,  52. 

95.  A.  D.  HALL  :  The  Soil. 

96.  SNYDER  :   Minnesota  Experiment  Station  Bulletin  No.  109. 

97.  KING  :  Investigations  in  Soil  Management. 

98.  Ohio  Agricultural  Experiment  Station  Bulletin  No.  no. 


INDEX 


Absorbents,  160. 

Absorption,  of  heat  by  soils,  47;    of 

gases  by  soils,  320. 
Absorptive  power  of  soils,  47,  51. 
Acid  phosphate,  preparation  of,  323. 
Acids  in  plant  roots,  258. 
Acid  soils,  1 01. 

Acid  soluble  matter  of  soils,  81,  320. 
Aeration  of  soils,  275. 
Aerobic  ferments,  177. 
Agricultural  geology,  54. 
Agronomy,  9. 
Air  and  soil  formation,  60. 
Air  movement  through  soils,  314. 
Albite,  65. 
Alchemy,  i. 
Alkaline  soils,  96. 
Alkali  soils,  improving,  99. 
Aluminum  of  soils,  78. 
Amendments,  soils,  233. 
Ammonium  compounds,  130. 
Ammonium  sulphate,  155. 
Anaerobic  ferments,  177. 
Analysis    of    soils,    how    made,    87; 

value  of,  88,  90;   interpretation  of, 

91-92. 

Apatite  rock,  67. 
Apparatus,  list  of,  308. 
Application,    of    fertilizer,    252;     of 

manures,  181,  184. 
Arrangement  of  soil  particles,  18. 
Ashes,  218;    action  of,  on  soils,  219; 

testing  of,  324. 
Assimilation,    of    nitrogen,    116;     of 

phosphates,  199. 
Atmospheric  nitrogen,  118. 
Atwater,  122,  151. 


Availability  of  plant  food,  92. 
Available  nitrogen,  128,  152. 
Available  phosphate,  203,  210. 

Bacterial  action  and  cultivation,  138, 

298. 
Barley,    fertilizers    for,    253;     food 

requirements  of,  261. 
Blood,  dried,  147. 
Bone,  dissolved,  208;    steamed,  208; 

fertilizers,  207. 
Bone  ash,  208. 
Bone  black,  209. 
Boussingault,  u,  119,  120. 
Buckwheat,  food  requirements  of,  266. 

Calcium  as  essential  element,  223. 

Calcium  carbonate,  and  -nitrification, 
140;  compounds  of  soils,  79;  ni- 
trate and  cyanamid,  156;  phos- 
phate, 68. 

Capillarity,  30;  and  cultivation,  36. 

Capillary  water,  determination  of, 
312. 

Carbon,  of  soil,  74;  sources  for  plant 
growth,  74. 

Cavendish,  2. 

Cereal  crops,  259. 

Chemical  composition  of  soils,  71. 

Chlorine  of  soil,  75. 

Citric  acid,  use  of,  in  soil  analysis,  84. 

Classification,  of  soils,  scheme  for, 
326;  of  elements,  71. 

Clay,  formation  of,  67;  particles,  16; 
sedimentation  of,  317. 

Clover,    as    manure,    154;     nitrogen 


345 


346 


INDEX 


returned  by,  122,  134,  289;  root 
nodules,  125;  manuring  of,  269. 

Coal  ashes,  220. 

Color,  of  plants,  influenced  by  nitro- 
gen, 118;  of  soils,  47,  50;  and  soil 
temperature,  314. 

Combination  of  elements  in  soils,  72. 

Commercial  fertilizers,  233,  254; 
abuse  of,  245;  and  tillage,  244; 
and  farm  manures,  254;  compo- 
sition of,  234;  extent  of  use,  233; 
field  tests  with,  248;  for  special 
crops,  253;  home  mixing  of,  243; 
inspection  of,  237;  judicious  use 
of,  246;  mechanical  condition  of, 
238 ;  misleading  statements,  241 ; 
nitrogen  of,  238;  phosphoric  acid 
of,  239;  plant  food  in,  237;  potash 
of,  240;  preparation  of,  234; 
valuation  of,  241 ;  variable  com- 
position, 234. 

Composition,  of  soils,  95,  97,  98;  of 
manures,  159. 

Composting  manures,  178. 

Corn,  fertilizers  for,  254;  food  re- 
quirements of,  263;  and  manure, 
185;  soils,  23. 

Cotton,  fertilizers  for,  267. 

Cottonseed  meal,  151. 

Cow  manure,  1 70. 

Crop  residue,  275. 

Cultivation,  after  rains,  38 ;  and  bac- 
terial action,  298;  shallow  surface, 
37;  and  soil  moisture,  313;  and 
soil  temperature,  49. 

Cumulative  fertility,  304. 

Cyanamid,  156. 

Davy,  work  of,  3. 

Deficiency,  of  nitrogen,  249;  of 
phosphoric  acid,  250;  of  potash, 
250;  of  two  elements,  250. 

Denitrification,  141. 

De  Saussure,  work  of,  3,  118. 

Dilute  mineral  acids,  action  of,  84. 


Diseases  of  soils,  301. 
Dissolved  bone,  208. 
Distribution  of  soils,  62. 
Drainage,  34,  47,  300. 
Dried  blood,  147. 

Early  truck  soils,  22. 
Earthworms,  61. 
Electricity  of  soil,  52. 
Evaporation,  53;    heat  required  for, 

46. 

Excessive  use  of  fertilizers,  252. 
Experimental  plots,  248. 
Experiments,  310,  325. 
Exposure  and  soil  temperature,  49. 

Fallow  fields,  145. 

Fall  plowing,  41. 

Farm  manures,  158,  189;  and  com- 
mercial fertilizers,  254. 

Feldspar,  64,  237. 

Fermentation  of  manures,  177. 

Fertility,  conservation  of,  285;  im- 
portance of,  305;  removed  in 
crops,  254. 

Fertilizers,  amount  to  use,  252;  in- 
fluence upon  soil  water,  44;  on 
barley,  253;  on  wheat,  253. 

Field  tests  with  fertilizers,  248. 

Fine  earth,  14. 

Fish  fertilizer,  151. 

Fixation,  191;  of  ammonia,  194;  of 
phosphates,  192;  of  potash,  192; 
due  to  zeolites,  191;  nitrates  not 
fixed,  193;  and  available  plant 
food,  194. 

Flax,  food  requiremerfts  of,  264;  soils, 
24. 

Flesh  meal,  150. 

Forest  fires,  1 1  r . 

Formation  of  soils,  54,  62. 

Form  of  soil  particles,  17. 

Fruit  soils,  23. 

Fruit  trees,  fertilizers  for,  270. 


INDEX 


347 


Gains,  of  humus,  114;    of  nitrogen, 

133- 

Garden  crops,  fertilizers  for,  269. 
Geological  study  of  soil,  value  of,  69. 
Gilbert,  7. 

Glaciers,  action  of,  57. 
Grain  soils,  24. 
Granite,  66. 

Grass  lands,  fertilizers  for,  268. 
Grass  soils,  24. 
Guano,  207. 
Gullying  of  soils,  300. 
Gypsum  and  manure,  179. 

Hair,  152. 

Hay  land,  fertilizing,  268. 

Heat,  and  crop  growth,  50;  pro- 
duced by  manures,  178;  of  soil,  46, 
50 ;  required  for  evaporation,  46. 

Heiden,  174,  180. 

Hellriegel,  22,  28,  123. 

Hen  manure,  172. 

Hog  manure,  172. 

Hops,  fertilizers  for,  267. 

Hornblende,  65. 

Horse  manure,  170. 

Human  excrements,  174. 

Humates,  103;   as  plant  food,  107. 

Humic  acid,  112. 

Humic  phosphates,  105,  210. 

Humification,  104. 

Humus,  103;  active  and  inactive,  114; 
causes  fixation,  192;  composition 
of,  1 06;  extraction  of,  from  soils, 
321;  loss  of,  from  soils,  in;  soils 
in  need  of,  113. 

Hydrogen,  compounds  of  soil,  77. 

Hydroscopic  moisture,  32;  deter- 
mination of,  310. 

Importance  of  field  trials,  251. 
Income  and  outgo  of  fertility,  286,  290. 
Infected  seed  and  soil  diseases,  301. 
Inherent  fertility,  304. 
Injury  of  coarse  manures,  46,  182. 


Inoculation  of  soils,  143. 
Insoluble  matters  of  soils,  82. 
Iron  compounds  of  soil,  80. 

Jenkins,  152. 

Kainit,  179,  216,  243. 
Kaolin,  67. 
King,  37,  40,  41. 

Laboratory  note-book,  307;   practice, 

308,  326. 

Lawes  and  Gilbert,  6,  121,  122,  260. 
Lawn  fertilizers,  272. 
Leached  ashes,  219. 
Leaching  of  manure,  175. 
Leather,  152. 
Leguminous    crops,     fertilizers    for, 

269;     as    manure,    154;     nitrogen 

assimilations  of,  122,  125. 
Liebig,  5,  6,  174,  257. 
Lime,  action  on  soils,  225;    amount 

of,  in  soils,  224;    amount  removed 

in  crops,  224;  excessive  use  of,  229; 

fertilizers,  225;    indirect  action  of, 

227;      physical     action     of,     228; 

stone,  68;    use  of,   229;    lime  and 

acid  soil,  226;    and  clover,  226. 
Liquid  manure,  164. 
Loam  soils,  27. 
Loss,  of  fertility  in  grain  fanning,  287 ; 

of  humus,   in;    of  nitrogen,   132, 

145- 
Losses  from  manures,  176-177. 

Magnesium  compounds  of  soils,  79. 

Magnesium  salts  as  fertilizers,  230. 

Mangels,  fertilizers  for,  254. 

Manure,  from  cow,  170;  hen,  172; 
hog,  172;  horse,  170;  sheep,  171. 

Manures,  farm,  158;  composition  of, 
159;  composting  of,  178;  crop 
producing  value,  168;  direct  ap- 
plication of,  181;  fermentation  of, 
177;  influence  of,  on  soil  tempera- 


348 


INDEX 


ture,  313;  on  moisture,  313;  in- 
fluenced by  foods,  162;  influenced 
by  age  and  kind  of  animal,  169; 
leaching  of,  175;  liquid,  164; 
mixing  of,  173;  solid,  164;  and 
soil  water,  45,  112;  and  tempera- 
ture, 48;  preservation  of,  175; 
use  of,  181,  184;  use  of,  in  rotation, 
278;  value  of,  189;  volatile  prod- 
ucts from,  173. 

Manurial  value  of  foods,  167. 

Manuring,  of  crops,  185;  pasture 
land,  183. 

Marl,  228. 

Mechanical,  analysis  of  soils,  19; 
condition  of  fertilizers,  238;  compo- 
sition of  soil  types,  27. 

Methods  of  farming,  influence  of, 
upon  fertility,  114. 

Mica,  66. 

Micro-organisms  and  soil  formation, 
54,  60. 

Mineral  matter  and  humus,  109. 

Mixing  manures,  1 73. 

Moisture  for  nitrification,  139. 

Movement  of  water  after  rains,  39. 

Muck,  153,  161. 

Mulching,  42. 

Nitrate  of  soda,  154. 

Nitric  nitrogen,  154. 

Nitrification,  135;  conditions  neces- 
sary for,  136;  elements  essential 
for,  140;  and  plowing,  145;  and 
sunlight,  139. 

Nitrogen,  assimilation,  118,  121;  of 
clover  plant,  122,  125;  as  plant 
food,  116;  compounds  of  soil,  76; 
compounds,  solubility  of,  323; 
deficiency  of,  in  soil,  249;  gain  of, 
in  soils,  133-134;  loss  of,  by 
fallowing,  144;  losses  of,  from  soil, 
132;  ratio  of,  to  carbon,  131;  re- 
moved in  crops,  128;  in  com- 
mercial fertilizers,  238;  in  rain 


water  and  snow,  131;    amount  of, 

in  soils,  128;  in  organic  forms,  127; 

as  nitrates,   129;  as    nitrites,    129; 

availability  of,  127;  forms  of,  126; 

origin  of,  126. 

Nitrogenous  manures,  146,  157. 
Number  of  soil  particles,  19. 

Oats,  food  requirements  of,  262. 

Odor  of  soils,  51. 

Organic  acids,  action  of,  upon  soils, 
84,  85. 

Organic  compounds  of  soil,  classifi- 
cation of,  103;  source  of,  102. 

Organic  nitrogen,  147,  152. 

Organisms,  ammonia- producing,  141 ; 
of  soil,  141;  nitrous  acid,  140; 
nitrifying,  137;  products  of,  142. 

Orthoclase,  65. 

Osborne,  20. 

Oxidation  of  soil,  48. 

Oxygen  compounds  of  soil,  77. 

Oxygen,  necessary  for  nitrification,  138. 

Pasteur,  8. 

Peat,  153,  161. 

Percolation,  32. 

Permanent  meadows,  manuring  of, 
268. 

Permeability  of  soils,  44. 

Phosphate  fertilizers,  198;  commer- 
cial forms,  201 ;  manufacture  of, 
204;  as  plant  food,  198;  removed 
by  crops,  199;  reverted,  202; 
rock,  203;  slag,  206;  use  of,  205. 

Phosphoric  acid,  of  commercial  fer- 
tilizers, 201,  239;  available,  198, 
203,  210;  acid  in  soils,  200;  defi- 
ciency of,  250;  removal  in  crops, 
199;  soluble  and  insoluble  in  soils, 
84;  testing  for,  323;  value  of,  205. 

Phosphorus  compounds  of  soils,  75. 

Physical,  analysis  of  soils,  316. 

Plant  food,  classes  of,  80;  ash  and 
fertilizers,  256;  distribution  of,  93, 


INDEX 


349 


94;  in  soil  solution,  81,  196;  total 
and  available,  92,  93. 

Plants,  crowding  of,  in  seed  bed,  302. 

Plowing,  depth  of,  43;  energy  re- 
quired for,  293 ;  fall,  41 ;  spring 
41 ;  influence  of,  on  soil,  291 ;  in- 
fluence of,  on  moisture,  294;  influ- 
ences nitrification,  291. 

Pore  space,  13. 

Potash  fertilizers,  212;  use  of,  222; 
of  commercial  fertilizers,  240 ;  salts, 
218. 

Potash,  in  soils,  amount  of,  214; 
sources  of,  215;  soluble  and  in- 
soluble, 84;  and  lime,  joint  use  of, 
222;  muriate  of,  217;  sulphate, 
217;  removed  in  crops,  213. 

Potassium  compounds  of  soil,  78. 

Potato,  fertilizers  for,  264;  food 
requirements  of,  264;  soils,  22. 

Preliminary  trials  with  fertilizers,  248. 

Priestley,  2. 

Property  of  soils,  12;  modified  by 
farming,  115. 

Pulverized  lime  rock,  227. 

Pulverizing  soils,  295. 

Quartz,  64. 
Questions,  327. 

Rainfall  and  crop  production,  29. 
Rape,  food  requirements  of,  266. 
Reaction  of  soils,  determination  of, 

3*9- 

References,  340,  344. 
Relation  of  crop  and  soil  type,  303. 
Reverted  phosphoric  acid,  202. 
Review  questions,  327. 
Roberts,  43.  J75»  293- 
Rock  disintegration,  55,  68. 
Rocks,  composition  of,  64,  69;   prop- 
erties of,  318. 
Rolling  of  soils,  40,  294. 
Root  crops,  fertilizers  for,  266. 
Roots,  action  on  soil,  255,  276. 


Rotation,  and  soil  water,  277;  and 
weeds,  280. 

Rotation  of  crops,  273,  284;  prin- 
ciples involved,  274;  length  of,  281 ; 
problems,  284;  and  farm  labor, 
278;  and  humus,  275;  and  insects, 
280;  and  soil  nitrogen,  276. 

Salt  as  a  fertilizer,  229. 

Sand,  grades  of,  14,  15. 

Schlosing,  8. 

Schubler,  5. 

Seaweeds  as  fertilizers,  231. 

Sedentary  soils,  62. 

Seed,  amount  of,  per  acre,  303.— 

Seed  bed,  preparation  of,  291.— 

Seed  residues,  151. 

Sheep  manure,  171. 

Silicon  and  silicates,  74. 

Silt  particles,  17. 

Size  of  soil  particles,  14. 

Skeleton  of  soils,  14. 

Small  fruits,  fertilizers  for,  271. 

Small  manure  piles,  183. 

Sodium  compounds  of  soils,  80. 

Sodium  nitrate,  154. 

Soil,  composition  of,  97,  98;  con- 
servation of  fertility,  Np85;  ex- 
haustion, 274,  304;  management, 
303;  particles,  study  of,  319;  sam- 
pling of,  86,  87 ;  solution  of,  80, 196; 
types,  21. 

Soils  and  agriculture,  relation  of,  305 ; 
crops  suitable  for,  303. 

Soot,  230. 

Specific  gravity  of  soil,  13. 

Specific  heat  of  soil,  48. 

Sprengel,  5. 

Spring  plowing,  41. 

Stassfurt  salts,  216. 

Stock  farming  and  fertility,  288. 

Storer,  75,  148. 

Strand's  plant  ash,  231. 

Street  sweepings,  232. 

Stutzer,  152. 


350 


INDEX 


Subsoiling,  40. 

Sugar  beets,  and  farm  manures,  185; 

fertilizers  for,  265. 
Sugar  beet  soils,  24. 
Sulphate  of  potash,  217. 
Sulphur  compounds  of  soil,  75. 
Superphosphates,  204. 
Surface  subsoil,  mixing  of,  297. 

Tankage,  149. 

Taste  of  soils,  51. 

Temperature  of  soils,  46. 

Testing  for  nitrates,  322. 

Tests  with  fertilizers,  248. 

Thaer,  work  of,  3. 

Tobacco,  manuring  of,  186. 

Tobacco  stems,  221. 

Transported  soils,  62. 

Truck  farming  and  fertilizers,  269. 

Tull,  8. 

Turnips,  fertilizers  for,  254,  266. 

Van  Helmont,  i. 

Vegetation  and  soil  formation,  61. 

Ville,  121. 

Volatilization  of  ammonium  salts,  322. 

Volcanic  soils,  64. 

Volume  of  soils,  13. 

Voorhees,  243,  269. 

Warington,  8,  139. 


Washing  of  land,  300. 

Water,  action  of,  upon  rocks  and 
soils,  56;  in  rock  decay,  59;  bot- 
tom, 29;  capillary,  30;  capillary 
conservation  of,  36-38. 

Water  holding,  capacity  of  soils,  311; 
hydroscopic,  32;  losses  by  evapo- 
ration, 33;  losses  by  percolation, 
32;  losses  by  transpiration,  34;  of 
soil,  29,  34;  of  soil  influenced  by 
drainage,  34;  by  forest  regions,  35; 
by  manures,  45;  by  mulching,  42; 
by  plowing,  41;  by  rolling,  40; 
by  subsoiling,  40;  required  by 
crops,  28;  soluble  matter  of  soils, 
196. 

Weeds,  cultivation  to  destroy,  297; 
fertility  in,  231. 

Weight  of  soils,  1 2 ;  how  determined, 

3*3- 
Wheat,     fertilizers    for,     253;     food 

requirements  of,  260;    soils,  25-26. 
Whitney,  19,  52. 
Wilfarth,  124. 

Wind  as  agent  in  soil  formation,  62. 
Winogradsky,  8. 
Wood  ashes,  218. 
Wool  waste,  152,  231. 

Zeolites,  67,  191. 


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Thomas  F.  Hunt's  How  to  Choose  a  Farm 

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Edward  B.  Voorhees's  Fertilizers 

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